Merge branch 'master' into all-contributors/add-charlesfinley

docs: update .all-contributorsrc [skip ci]
docs: update README.md [skip ci]
2020-08-03 16:34:41 +03:00 · 2020-08-03 13:30:52 +00:00 · 2020-08-03 13:30:51 +00:00 · 2020-08-02 22:48:54 +03:00 · 2020-08-02 11:55:13 +03:00 · 2020-08-02 11:51:14 +03:00
284 changed files with 2536 additions and 2061 deletions
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@ -191,9 +191,893 @@
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--- a/README.md
+++ b/README.md
@ -9,7 +9,7 @@
 [![Join the chat at https://gitter.im/iluwatar/java-design-patterns](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Sonarcloud Status](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=alert_status)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns) 
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-20-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-118-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->

 # Introduction
@ -73,31 +73,182 @@ This project is licensed under the terms of the MIT license.
    <td align="center"><a href="https://github.com/amit1307"><img src="https://avatars0.githubusercontent.com/u/23420222?v=4" width="100px;" alt=""/><br /><sub><b>amit1307</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amit1307" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/npathai"><img src="https://avatars2.githubusercontent.com/u/1792515?v=4" width="100px;" alt=""/><br /><sub><b>Narendra Pathai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=npathai" title="Code">💻</a> <a href="#ideas-npathai" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Anpathai" title="Reviewed Pull Requests">👀</a></td>
    <td align="center"><a href="https://github.com/fluxw42"><img src="https://avatars1.githubusercontent.com/u/1545460?v=4" width="100px;" alt=""/><br /><sub><b>Jeroen Meulemeester</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=fluxw42" title="Code">💻</a></td>
+  </tr>
+  <tr>
    <td align="center"><a href="http://www.joemccarthy.co.uk"><img src="https://avatars0.githubusercontent.com/u/4526195?v=4" width="100px;" alt=""/><br /><sub><b>Joseph McCarthy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mikulucky" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/thomasoss"><img src="https://avatars1.githubusercontent.com/u/22516154?v=4" width="100px;" alt=""/><br /><sub><b>Thomas</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=thomasoss" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/anuragagarwal561994"><img src="https://avatars1.githubusercontent.com/u/6075379?v=4" width="100px;" alt=""/><br /><sub><b>Anurag Agarwal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=anuragagarwal561994" title="Code">💻</a></td>
+    <td align="center"><a href="https://markusmo3.github.io"><img src="https://avatars1.githubusercontent.com/u/3317416?v=4" width="100px;" alt=""/><br /><sub><b>Markus Moser</b></sub></a><br /><a href="#design-markusmo3" title="Design">🎨</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=markusmo3" title="Code">💻</a> <a href="#ideas-markusmo3" title="Ideas, Planning, & Feedback">🤔</a></td>
  </tr>
  <tr>
-    <td align="center"><a href="https://markusmo3.github.io"><img src="https://avatars1.githubusercontent.com/u/3317416?v=4" width="100px;" alt=""/><br /><sub><b>Markus Moser</b></sub></a><br /><a href="#design-markusmo3" title="Design">🎨</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=markusmo3" title="Code">💻</a> <a href="#ideas-markusmo3" title="Ideas, Planning, & Feedback">🤔</a></td>
    <td align="center"><a href="https://twitter.com/i_sabiq"><img src="https://avatars1.githubusercontent.com/u/19510920?v=4" width="100px;" alt=""/><br /><sub><b>Sabiq Ihab</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=isabiq" title="Code">💻</a></td>
    <td align="center"><a href="http://inbravo.github.io"><img src="https://avatars3.githubusercontent.com/u/5253764?v=4" width="100px;" alt=""/><br /><sub><b>Amit Dixit</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=inbravo" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/piyushchaudhari04"><img src="https://avatars3.githubusercontent.com/u/10268029?v=4" width="100px;" alt=""/><br /><sub><b>Piyush Kailash Chaudhari</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=piyushchaudhari04" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/joshzambales"><img src="https://avatars1.githubusercontent.com/u/8704552?v=4" width="100px;" alt=""/><br /><sub><b>joshzambales</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=joshzambales" title="Code">💻</a></td>
-    <td align="center"><a href="https://github.com/Crossy147"><img src="https://avatars2.githubusercontent.com/u/7272996?v=4" width="100px;" alt=""/><br /><sub><b>Kamil Pietruszka</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Crossy147" title="Code">💻</a></td>
-    <td align="center"><a href="http://cs.joensuu.fi/~zkhayda"><img src="https://avatars2.githubusercontent.com/u/660742?v=4" width="100px;" alt=""/><br /><sub><b>Zafar Khaydarov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Documentation">📖</a></td>
  </tr>
  <tr>
+    <td align="center"><a href="https://github.com/Crossy147"><img src="https://avatars2.githubusercontent.com/u/7272996?v=4" width="100px;" alt=""/><br /><sub><b>Kamil Pietruszka</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Crossy147" title="Code">💻</a></td>
+    <td align="center"><a href="http://cs.joensuu.fi/~zkhayda"><img src="https://avatars2.githubusercontent.com/u/660742?v=4" width="100px;" alt=""/><br /><sub><b>Zafar Khaydarov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Documentation">📖</a></td>
    <td align="center"><a href="https://kemitix.github.io/"><img src="https://avatars1.githubusercontent.com/u/1147749?v=4" width="100px;" alt=""/><br /><sub><b>Paul Campbell</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kemitix" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/Argyro-Sioziou"><img src="https://avatars0.githubusercontent.com/u/22822639?v=4" width="100px;" alt=""/><br /><sub><b>Argyro Sioziou</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Argyro-Sioziou" title="Code">💻</a></td>
+  </tr>
+  <tr>
    <td align="center"><a href="https://github.com/TylerMcConville"><img src="https://avatars0.githubusercontent.com/u/4946449?v=4" width="100px;" alt=""/><br /><sub><b>TylerMcConville</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=TylerMcConville" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/saksham93"><img src="https://avatars1.githubusercontent.com/u/37399540?v=4" width="100px;" alt=""/><br /><sub><b>saksham93</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=saksham93" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/nikhilbarar"><img src="https://avatars2.githubusercontent.com/u/37332144?v=4" width="100px;" alt=""/><br /><sub><b>nikhilbarar</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=nikhilbarar" title="Code">💻</a></td>
    <td align="center"><a href="http://colinbut.com"><img src="https://avatars2.githubusercontent.com/u/10725674?v=4" width="100px;" alt=""/><br /><sub><b>Colin But</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=colinbut" title="Code">💻</a></td>
  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ruslanpa"><img src="https://avatars2.githubusercontent.com/u/1503411?v=4" width="100px;" alt=""/><br /><sub><b>Ruslan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ruslanpa" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/JuhoKang"><img src="https://avatars1.githubusercontent.com/u/4745294?v=4" width="100px;" alt=""/><br /><sub><b>Juho Kang</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=JuhoKang" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dheeraj-mummareddy"><img src="https://avatars2.githubusercontent.com/u/7002230?v=4" width="100px;" alt=""/><br /><sub><b>Dheeraj Mummareddy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dheeraj-mummareddy" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.bernardosulzbach.com"><img src="https://avatars0.githubusercontent.com/u/8271090?v=4" width="100px;" alt=""/><br /><sub><b>Bernardo Sulzbach</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=bernardosulzbach" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/4lexis"><img src="https://avatars0.githubusercontent.com/u/19871727?v=4" width="100px;" alt=""/><br /><sub><b>Aleksandar Dudukovic</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=4lexis" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.yusufaytas.com"><img src="https://avatars2.githubusercontent.com/u/1049483?v=4" width="100px;" alt=""/><br /><sub><b>Yusuf Aytaş</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yusufaytas" title="Code">💻</a></td>
+    <td align="center"><a href="http://futurehomes.hu"><img src="https://avatars2.githubusercontent.com/u/1001491?v=4" width="100px;" alt=""/><br /><sub><b>Mihály Kuprivecz</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=qpi" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/kapinuss"><img src="https://avatars0.githubusercontent.com/u/17639945?v=4" width="100px;" alt=""/><br /><sub><b>Stanislav Kapinus</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kapinuss" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/gvsharma"><img src="https://avatars1.githubusercontent.com/u/6648152?v=4" width="100px;" alt=""/><br /><sub><b>GVSharma</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=gvsharma" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/SrdjanPaunovic"><img src="https://avatars1.githubusercontent.com/u/22815104?v=4" width="100px;" alt=""/><br /><sub><b>Srđan Paunović</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=SrdjanPaunovic" title="Code">💻</a></td>
+    <td align="center"><a href="https://sideris.xyz/"><img src="https://avatars3.githubusercontent.com/u/5484694?v=4" width="100px;" alt=""/><br /><sub><b>Petros G. Sideris</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sideris" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/pramodgupta3/"><img src="https://avatars1.githubusercontent.com/u/2184241?v=4" width="100px;" alt=""/><br /><sub><b>Pramod Gupta</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AIAmPramod" title="Reviewed Pull Requests">👀</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://amarnath510.github.io/portfolio"><img src="https://avatars0.githubusercontent.com/u/4599623?v=4" width="100px;" alt=""/><br /><sub><b>Amarnath Chandana</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Amarnath510" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Anurag870"><img src="https://avatars1.githubusercontent.com/u/6295975?v=4" width="100px;" alt=""/><br /><sub><b>Anurag870</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Anurag870" title="Code">💻</a></td>
+    <td align="center"><a href="http://theerroris.me"><img src="https://avatars0.githubusercontent.com/u/1685953?v=4" width="100px;" alt=""/><br /><sub><b>Wes Gilleland</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Deathnerd" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Harshrajsinh"><img src="https://avatars2.githubusercontent.com/u/22811531?v=4" width="100px;" alt=""/><br /><sub><b>Harshraj Thakor</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Harshrajsinh" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/MaVdbussche"><img src="https://avatars1.githubusercontent.com/u/26136934?v=4" width="100px;" alt=""/><br /><sub><b>Martin Vandenbussche</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=MaVdbussche" title="Code">💻</a></td>
+    <td align="center"><a href="https://alexsomai.com"><img src="https://avatars1.githubusercontent.com/u/5720977?v=4" width="100px;" alt=""/><br /><sub><b>Alexandru Somai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=alexsomai" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/amogozov"><img src="https://avatars3.githubusercontent.com/u/7372215?v=4" width="100px;" alt=""/><br /><sub><b>Artur Mogozov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amogozov" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/anthonycampbell"><img src="https://avatars3.githubusercontent.com/u/10249255?v=4" width="100px;" alt=""/><br /><sub><b>anthony</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=anthonycampbell" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://ccygnus.com/"><img src="https://avatars1.githubusercontent.com/u/9342724?v=4" width="100px;" alt=""/><br /><sub><b>Christian Cygnus</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=christophercolumbusdog" title="Code">💻</a></td>
+    <td align="center"><a href="https://about.me/dzmitryh"><img src="https://avatars2.githubusercontent.com/u/5390492?v=4" width="100px;" alt=""/><br /><sub><b>Dima Gubin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dzmitryh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/jjjimenez100"><img src="https://avatars3.githubusercontent.com/u/22243493?v=4" width="100px;" alt=""/><br /><sub><b>Joshua Jimenez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=jjjimenez100" title="Code">💻</a></td>
+    <td align="center"><a href="http://about.me/kaiwinter"><img src="https://avatars0.githubusercontent.com/u/110982?v=4" width="100px;" alt=""/><br /><sub><b>Kai Winter</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kaiwinter" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/lbroman"><img src="https://avatars1.githubusercontent.com/u/86007?v=4" width="100px;" alt=""/><br /><sub><b>lbroman</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=lbroman" title="Code">💻</a></td>
+    <td align="center"><a href="https://przemeknowak.com"><img src="https://avatars1.githubusercontent.com/u/3254609?v=4" width="100px;" alt=""/><br /><sub><b>Przemek</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=pnowy" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/prafful1"><img src="https://avatars0.githubusercontent.com/u/14350274?v=4" width="100px;" alt=""/><br /><sub><b>Prafful Agarwal</b></sub></a><br /><a href="#content-prafful1" title="Content">🖋</a></td>
+    <td align="center"><a href="https://github.com/sankypanhale"><img src="https://avatars1.githubusercontent.com/u/6478783?v=4" width="100px;" alt=""/><br /><sub><b>Sanket Panhale</b></sub></a><br /><a href="#content-sankypanhale" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/staillebois"><img src="https://avatars0.githubusercontent.com/u/23701200?v=4" width="100px;" alt=""/><br /><sub><b>staillebois</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=staillebois" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/valdar-hu"><img src="https://avatars3.githubusercontent.com/u/17962817?v=4" width="100px;" alt=""/><br /><sub><b>Krisztián Nagy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=valdar-hu" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.vanogrid.com"><img src="https://avatars0.githubusercontent.com/u/4307918?v=4" width="100px;" alt=""/><br /><sub><b>Alexander Ivanov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vanogrid" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/yosfik"><img src="https://avatars3.githubusercontent.com/u/4850270?v=4" width="100px;" alt=""/><br /><sub><b>Yosfik Alqadri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yosfik" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/7agustibm"><img src="https://avatars0.githubusercontent.com/u/8149332?v=4" width="100px;" alt=""/><br /><sub><b>Agustí Becerra Milà</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=7agustibm" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Juaanma"><img src="https://avatars3.githubusercontent.com/u/7390500?v=4" width="100px;" alt=""/><br /><sub><b>Juan Manuel Suárez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Juaanma" title="Code">💻</a></td>
+    <td align="center"><a href="http://www.devsedge.net/"><img src="https://avatars0.githubusercontent.com/u/9956006?v=4" width="100px;" alt=""/><br /><sub><b>Luigi Cortese</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=LuigiCortese" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Rzeposlaw"><img src="https://avatars2.githubusercontent.com/u/18425745?v=4" width="100px;" alt=""/><br /><sub><b>Katarzyna Rzepecka</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Rzeposlaw" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://adamski.pro"><img src="https://avatars1.githubusercontent.com/u/6537430?v=4" width="100px;" alt=""/><br /><sub><b>adamski.pro</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=akrystian" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/baislsl"><img src="https://avatars0.githubusercontent.com/u/17060584?v=4" width="100px;" alt=""/><br /><sub><b>Shengli Bai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=baislsl" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/besok"><img src="https://avatars2.githubusercontent.com/u/29834592?v=4" width="100px;" alt=""/><br /><sub><b>Boris</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=besok" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dmitraver"><img src="https://avatars3.githubusercontent.com/u/1798156?v=4" width="100px;" alt=""/><br /><sub><b>Dmitry Avershin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dmitraver" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/fanofxiaofeng"><img src="https://avatars0.githubusercontent.com/u/3983683?v=4" width="100px;" alt=""/><br /><sub><b>靳阳</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=fanofxiaofeng" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hoangnam2261"><img src="https://avatars2.githubusercontent.com/u/31692990?v=4" width="100px;" alt=""/><br /><sub><b>hoangnam2261</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hoangnam2261" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/jarpit96"><img src="https://avatars2.githubusercontent.com/u/10098713?v=4" width="100px;" alt=""/><br /><sub><b>Arpit Jain</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=jarpit96" title="Code">💻</a></td>
+    <td align="center"><a href="http://joningi.net"><img src="https://avatars2.githubusercontent.com/u/6115148?v=4" width="100px;" alt=""/><br /><sub><b>Jón Ingi Sveinbjörnsson</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=joningiwork" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/kirill-vlasov"><img src="https://avatars3.githubusercontent.com/u/16112495?v=4" width="100px;" alt=""/><br /><sub><b>Kirill Vlasov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kirill-vlasov" title="Code">💻</a></td>
+    <td align="center"><a href="http://mitchell-irvin.com"><img src="https://avatars0.githubusercontent.com/u/16233245?v=4" width="100px;" alt=""/><br /><sub><b>Mitchell Irvin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mitchellirvin" title="Code">💻</a></td>
+    <td align="center"><a href="https://ranjeet-floyd.github.io"><img src="https://avatars0.githubusercontent.com/u/1992972?v=4" width="100px;" alt=""/><br /><sub><b>Ranjeet</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ranjeet-floyd" title="Code">💻</a></td>
+    <td align="center"><a href="https://alwayswithme.github.io"><img src="https://avatars3.githubusercontent.com/u/3234786?v=4" width="100px;" alt=""/><br /><sub><b>PhoenixYip</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Alwayswithme" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/MSaifAsif"><img src="https://avatars1.githubusercontent.com/u/6280554?v=4" width="100px;" alt=""/><br /><sub><b>M Saif Asif</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=MSaifAsif" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/kanwarpreet25"><img src="https://avatars0.githubusercontent.com/u/39183641?v=4" width="100px;" alt=""/><br /><sub><b>kanwarpreet25</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kanwarpreet25" title="Code">💻</a></td>
+    <td align="center"><a href="http://leonmak.me"><img src="https://avatars3.githubusercontent.com/u/13071508?v=4" width="100px;" alt=""/><br /><sub><b>Leon Mak</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=leonmak" title="Code">💻</a></td>
+    <td align="center"><a href="http://www.wramdemark.se"><img src="https://avatars2.githubusercontent.com/u/7052193?v=4" width="100px;" alt=""/><br /><sub><b>Per Wramdemark</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=perwramdemark" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/waisuan"><img src="https://avatars2.githubusercontent.com/u/10975700?v=4" width="100px;" alt=""/><br /><sub><b>Evan Sia Wai Suan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=waisuan" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/AnaghaSasikumar"><img src="https://avatars2.githubusercontent.com/u/42939261?v=4" width="100px;" alt=""/><br /><sub><b>AnaghaSasikumar</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=AnaghaSasikumar" title="Code">💻</a></td>
+    <td align="center"><a href="https://christofferh.com"><img src="https://avatars1.githubusercontent.com/u/767643?v=4" width="100px;" alt=""/><br /><sub><b>Christoffer Hamberg</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=christofferh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dgruntz"><img src="https://avatars0.githubusercontent.com/u/1516800?v=4" width="100px;" alt=""/><br /><sub><b>Dominik Gruntz</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dgruntz" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://bitbucket.org/hannespernpeintner/"><img src="https://avatars3.githubusercontent.com/u/1679437?v=4" width="100px;" alt=""/><br /><sub><b>Hannes</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hannespernpeintner" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/leogtzr"><img src="https://avatars0.githubusercontent.com/u/1211969?v=4" width="100px;" alt=""/><br /><sub><b>Leo Gutiérrez Ramírez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=leogtzr" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/npczwh"><img src="https://avatars0.githubusercontent.com/u/14066422?v=4" width="100px;" alt=""/><br /><sub><b>Zhang WH</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=npczwh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/oconnelc"><img src="https://avatars0.githubusercontent.com/u/1112973?v=4" width="100px;" alt=""/><br /><sub><b>Christopher O'Connell</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=oconnelc" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/giorgosmav21"><img src="https://avatars2.githubusercontent.com/u/22855493?v=4" width="100px;" alt=""/><br /><sub><b>George Mavroeidis</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=giorgosmav21" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hbothra15"><img src="https://avatars1.githubusercontent.com/u/7418012?v=4" width="100px;" alt=""/><br /><sub><b>Hemant Bothra</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hbothra15" title="Code">💻</a> <a href="#design-hbothra15" title="Design">🎨</a></td>
+    <td align="center"><a href="https://www.kevinpeters.net/about/"><img src="https://avatars1.githubusercontent.com/u/12736734?v=4" width="100px;" alt=""/><br /><sub><b>Kevin Peters</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=igeligel" title="Code">💻</a></td>
+    <td align="center"><a href="https://llorllale.github.io/"><img src="https://avatars1.githubusercontent.com/u/2019896?v=4" width="100px;" alt=""/><br /><sub><b>George Aristy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=llorllale" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/mookkiah"><img src="https://avatars1.githubusercontent.com/u/8975264?v=4" width="100px;" alt=""/><br /><sub><b>Mahendran Mookkiah</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mookkiah" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Azureyjt"><img src="https://avatars2.githubusercontent.com/u/18476317?v=4" width="100px;" alt=""/><br /><sub><b>Azureyjt</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Azureyjt" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/vehpsr"><img src="https://avatars2.githubusercontent.com/u/3133265?v=4" width="100px;" alt=""/><br /><sub><b>gans</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vehpsr" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/ThatGuyWithTheHat"><img src="https://avatars0.githubusercontent.com/u/24470582?v=4" width="100px;" alt=""/><br /><sub><b>Matt</b></sub></a><br /><a href="#content-ThatGuyWithTheHat" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://www.linkedin.com/in/gopinathlangote/"><img src="https://avatars2.githubusercontent.com/u/10210778?v=4" width="100px;" alt=""/><br /><sub><b>Gopinath Langote</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=gopinath-langote" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hoswey"><img src="https://avatars3.githubusercontent.com/u/3689445?v=4" width="100px;" alt=""/><br /><sub><b>Hoswey</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hoswey" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/amit2103"><img src="https://avatars3.githubusercontent.com/u/7566692?v=4" width="100px;" alt=""/><br /><sub><b>Amit Pandey</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amit2103" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/gwildor28"><img src="https://avatars0.githubusercontent.com/u/16000365?v=4" width="100px;" alt=""/><br /><sub><b>gwildor28</b></sub></a><br /><a href="#content-gwildor28" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://t.me/paul_docker"><img src="https://avatars1.githubusercontent.com/u/2404785?v=4" width="100px;" alt=""/><br /><sub><b>田浩</b></sub></a><br /><a href="#content-llitfkitfk" title="Content">🖋</a></td>
+    <td align="center"><a href="https://twitter.com/StPitsios"><img src="https://avatars1.githubusercontent.com/u/6773603?v=4" width="100px;" alt=""/><br /><sub><b>Stamatis Pitsios</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=pitsios-s" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/qza"><img src="https://avatars3.githubusercontent.com/u/233149?v=4" width="100px;" alt=""/><br /><sub><b>qza</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=qza" title="Code">💻</a></td>
+    <td align="center"><a href="http://tschis.github.io"><img src="https://avatars1.githubusercontent.com/u/20662669?v=4" width="100px;" alt=""/><br /><sub><b>Rodolfo Forte</b></sub></a><br /><a href="#content-Tschis" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ankurkaushal"><img src="https://avatars2.githubusercontent.com/u/2236616?v=4" width="100px;" alt=""/><br /><sub><b>Ankur Kaushal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ankurkaushal" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/ovidijus-okinskas/"><img src="https://avatars0.githubusercontent.com/u/20372387?v=4" width="100px;" alt=""/><br /><sub><b>Ovidijus Okinskas</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=okinskas" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/robertt240"><img src="https://avatars1.githubusercontent.com/u/9137432?v=4" width="100px;" alt=""/><br /><sub><b>Robert Kasperczyk</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=robertt240" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/trautonen"><img src="https://avatars3.githubusercontent.com/u/1641063?v=4" width="100px;" alt=""/><br /><sub><b>Tapio Rautonen</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=trautonen" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://vk.com/yuri.orlov"><img src="https://avatars0.githubusercontent.com/u/1595733?v=4" width="100px;" alt=""/><br /><sub><b>Yuri Orlov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yorlov" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/varunu28/"><img src="https://avatars0.githubusercontent.com/u/7676016?v=4" width="100px;" alt=""/><br /><sub><b>Varun Upadhyay</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=varunu28" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/PalAditya"><img src="https://avatars2.githubusercontent.com/u/25523604?v=4" width="100px;" alt=""/><br /><sub><b>Aditya Pal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=PalAditya" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/grzesiekkedzior"><img src="https://avatars3.githubusercontent.com/u/23739158?v=4" width="100px;" alt=""/><br /><sub><b>grzesiekkedzior</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=grzesiekkedzior" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/sivasubramanim"><img src="https://avatars2.githubusercontent.com/u/51107434?v=4" width="100px;" alt=""/><br /><sub><b>Sivasubramani M</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sivasubramanim" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/d4gg4d"><img src="https://avatars2.githubusercontent.com/u/99457?v=4" width="100px;" alt=""/><br /><sub><b>Sami Airaksinen</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=d4gg4d" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/vertti"><img src="https://avatars0.githubusercontent.com/u/557751?v=4" width="100px;" alt=""/><br /><sub><b>Janne Sinivirta</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vertti" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Bobo1239"><img src="https://avatars1.githubusercontent.com/u/2302947?v=4" width="100px;" alt=""/><br /><sub><b>Boris-Chengbiao Zhou</b></sub></a><br /><a href="#content-Bobo1239" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://jahhein.github.io"><img src="https://avatars2.githubusercontent.com/u/10779515?v=4" width="100px;" alt=""/><br /><sub><b>Jacob Hein</b></sub></a><br /><a href="#content-Jahhein" title="Content">🖋</a></td>
+    <td align="center"><a href="https://github.com/iamrichardjones"><img src="https://avatars3.githubusercontent.com/u/14842151?v=4" width="100px;" alt=""/><br /><sub><b>Richard Jones</b></sub></a><br /><a href="#content-iamrichardjones" title="Content">🖋</a></td>
+    <td align="center"><a href="https://rachelcarmena.github.io"><img src="https://avatars0.githubusercontent.com/u/22792183?v=4" width="100px;" alt=""/><br /><sub><b>Rachel M. Carmena</b></sub></a><br /><a href="#content-rachelcarmena" title="Content">🖋</a></td>
+    <td align="center"><a href="https://zd-zero.github.io"><img src="https://avatars0.githubusercontent.com/u/21978370?v=4" width="100px;" alt=""/><br /><sub><b>Zaerald Denze Lungos</b></sub></a><br /><a href="#content-zd-zero" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://webpro.nl"><img src="https://avatars1.githubusercontent.com/u/456426?v=4" width="100px;" alt=""/><br /><sub><b>Lars Kappert</b></sub></a><br /><a href="#content-webpro" title="Content">🖋</a></td>
+    <td align="center"><a href="https://xiaod.info"><img src="https://avatars2.githubusercontent.com/u/21277644?v=4" width="100px;" alt=""/><br /><sub><b>Mike Liu</b></sub></a><br /><a href="#translation-xiaod-dev" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/charlesfinley"><img src="https://avatars1.githubusercontent.com/u/6307904?v=4" width="100px;" alt=""/><br /><sub><b>Matt Dolan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=charlesfinley" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/MananS77"><img src="https://avatars3.githubusercontent.com/u/21033516?v=4" width="100px;" alt=""/><br /><sub><b>Manan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AMananS77" title="Reviewed Pull Requests">👀</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/nishant"><img src="https://avatars2.githubusercontent.com/u/15331971?v=4" width="100px;" alt=""/><br /><sub><b>Nishant Arora</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=nishant" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/raja-peeyush-kumar-singh"><img src="https://avatars0.githubusercontent.com/u/5496024?v=4" width="100px;" alt=""/><br /><sub><b>Peeyush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=raja-peeyush-kumar-singh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/charlesfinley"><img src="https://avatars1.githubusercontent.com/u/6307904?v=4" width="100px;" alt=""/><br /><sub><b>Matt Dolan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=charlesfinley" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Acharlesfinley" title="Reviewed Pull Requests">👀</a></td>
+  </tr>
 </table>

 <!-- markdownlint-enable -->
 <!-- prettier-ignore-end -->
 <!-- ALL-CONTRIBUTORS-LIST:END -->
-
-This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!
--- a/abstract-document/README.md
+++ b/abstract-document/README.md
@ -9,21 +9,182 @@ tags:
 ---

 ## Intent
-Achieve flexibility of untyped languages and keep the type-safety 
+
+Use dynamic properties and achieve flexibility of untyped languages while keeping type-safety. 
+
+## Explanation
+
+The Abstract Document pattern enables handling additional, non-static properties. This pattern
+uses concept of traits to enable type safety and separate properties of different classes into
+set of interfaces.
+
+Real world example
+
+>  Consider a car that consists of multiple parts. However we don't know if the specific car really has all the parts, or just some of them. Our cars are dynamic and extremely flexible.
+
+In plain words
+
+> Abstract Document pattern allows attaching properties to objects without them knowing about it.
+
+Wikipedia says
+
+> An object-oriented structural design pattern for organizing objects in loosely typed key-value stores and exposing 
+the data using typed views. The purpose of the pattern is to achieve a high degree of flexibility between components 
+in a strongly typed language where new properties can be added to the object-tree on the fly, without losing the 
+support of type-safety. The pattern makes use of traits to separate different properties of a class into different 
+interfaces.
+
+**Programmatic Example**
+
+Let's first define the base classes `Document` and `AbstractDocument`. They basically make the object hold a property
+map and any amount of child objects.
+
+```java
+public interface Document {
+
+  Void put(String key, Object value);
+
+  Object get(String key);
+
+  <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor);
+}
+
+public abstract class AbstractDocument implements Document {
+
+  private final Map<String, Object> properties;
+
+  protected AbstractDocument(Map<String, Object> properties) {
+    Objects.requireNonNull(properties, "properties map is required");
+    this.properties = properties;
+  }
+
+  @Override
+  public Void put(String key, Object value) {
+    properties.put(key, value);
+    return null;
+  }
+
+  @Override
+  public Object get(String key) {
+    return properties.get(key);
+  }
+
+  @Override
+  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
+    return Stream.ofNullable(get(key))
+        .filter(Objects::nonNull)
+        .map(el -> (List<Map<String, Object>>) el)
+        .findAny()
+        .stream()
+        .flatMap(Collection::stream)
+        .map(constructor);
+  }
+  ...
+}
+```
+Next we define an enum `Property` and a set of interfaces for type, price, model and parts. This allows us to create
+static looking interface to our `Car` class.
+
+```java
+public enum Property {
+
+  PARTS, TYPE, PRICE, MODEL
+}
+
+public interface HasType extends Document {
+
+  default Optional<String> getType() {
+    return Optional.ofNullable((String) get(Property.TYPE.toString()));
+  }
+}
+
+public interface HasPrice extends Document {
+
+  default Optional<Number> getPrice() {
+    return Optional.ofNullable((Number) get(Property.PRICE.toString()));
+  }
+}
+public interface HasModel extends Document {
+
+  default Optional<String> getModel() {
+    return Optional.ofNullable((String) get(Property.MODEL.toString()));
+  }
+}
+
+public interface HasParts extends Document {
+
+  default Stream<Part> getParts() {
+    return children(Property.PARTS.toString(), Part::new);
+  }
+}
+```
+
+Now we are ready to introduce the `Car`.
+
+```java
+public class Car extends AbstractDocument implements HasModel, HasPrice, HasParts {
+
+  public Car(Map<String, Object> properties) {
+    super(properties);
+  }
+}
+```
+
+And finally here's how we construct and use the `Car` in a full example.
+
+```java
+    LOGGER.info("Constructing parts and car");
+
+    var wheelProperties = Map.of(
+        Property.TYPE.toString(), "wheel",
+        Property.MODEL.toString(), "15C",
+        Property.PRICE.toString(), 100L);
+
+    var doorProperties = Map.of(
+        Property.TYPE.toString(), "door",
+        Property.MODEL.toString(), "Lambo",
+        Property.PRICE.toString(), 300L);
+
+    var carProperties = Map.of(
+        Property.MODEL.toString(), "300SL",
+        Property.PRICE.toString(), 10000L,
+        Property.PARTS.toString(), List.of(wheelProperties, doorProperties));
+
+    var car = new Car(carProperties);
+
+    LOGGER.info("Here is our car:");
+    LOGGER.info("-> model: {}", car.getModel().orElseThrow());
+    LOGGER.info("-> price: {}", car.getPrice().orElseThrow());
+    LOGGER.info("-> parts: ");
+    car.getParts().forEach(p -> LOGGER.info("\t{}/{}/{}",
+        p.getType().orElse(null),
+        p.getModel().orElse(null),
+        p.getPrice().orElse(null))
+    );
+
+    // Constructing parts and car
+    // Here is our car:
+    // model: 300SL
+    // price: 10000
+    // parts: 
+    // wheel/15C/100
+    // door/Lambo/300
+```

 ## Class diagram
+
 ![alt text](./etc/abstract-document.png "Abstract Document Traits and Domain")

-
 ## Applicability
+
 Use the Abstract Document Pattern when

-* there is a need to add new properties on the fly
-* you want a flexible way to organize domain in tree like structure
-* you want more loosely coupled system
-
+* There is a need to add new properties on the fly
+* You want a flexible way to organize domain in tree like structure
+* You want more loosely coupled system

 ## Credits

 * [Wikipedia: Abstract Document Pattern](https://en.wikipedia.org/wiki/Abstract_Document_Pattern)
 * [Martin Fowler: Dealing with properties](http://martinfowler.com/apsupp/properties.pdf)
+* [Pattern-Oriented Software Architecture Volume 4: A Pattern Language for Distributed Computing (v. 4)](https://www.amazon.com/gp/product/0470059028/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0470059028&linkId=e3aacaea7017258acf184f9f3283b492)
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/App.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/App.java
@ -43,9 +43,11 @@ public class App {
  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

  /**
-   * Executes the App.
+   * Program entry point.
+   *
+   * @param args command line args
   */
-  public App() {
+  public static void main(String[] args) {
    LOGGER.info("Constructing parts and car");

    var wheelProperties = Map.of(
@ -75,14 +77,4 @@ public class App {
        p.getPrice().orElse(null))
    );
  }
-
-  /**
-   * Program entry point.
-   *
-   * @param args command line args
-   */
-  public static void main(String[] args) {
-    new App();
-  }
-
 }
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasParts.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasParts.java
@ -32,7 +32,6 @@ import java.util.stream.Stream;
 */
 public interface HasParts extends Document {

-
  default Stream<Part> getParts() {
    return children(Property.PARTS.toString(), Part::new);
  }
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasPrice.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasPrice.java
@ -32,7 +32,6 @@ import java.util.Optional;
 */
 public interface HasPrice extends Document {

-
  default Optional<Number> getPrice() {
    return Optional.ofNullable((Number) get(Property.PRICE.toString()));
  }
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasType.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasType.java
@ -32,7 +32,6 @@ import java.util.Optional;
 */
 public interface HasType extends Document {

-
  default Optional<String> getType() {
    return Optional.ofNullable((String) get(Property.TYPE.toString()));
  }
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/module-info.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.abstractdocument {
-	requires org.slf4j;
-}
--- a/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java
+++ b/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java
@ -40,14 +40,14 @@ public class AbstractDocumentTest {
  private static final String KEY = "key";
  private static final String VALUE = "value";

-  private class DocumentImplementation extends AbstractDocument {
+  private static class DocumentImplementation extends AbstractDocument {

    DocumentImplementation(Map<String, Object> properties) {
      super(properties);
    }
  }

-  private DocumentImplementation document = new DocumentImplementation(new HashMap<>());
+  private final DocumentImplementation document = new DocumentImplementation(new HashMap<>());

  @Test
  public void shouldPutAndGetValue() {
--- a/abstract-factory/README.md
+++ b/abstract-factory/README.md
@ -9,13 +9,16 @@ tags:
 ---

 ## Also known as
+
 Kit

 ## Intent
+
 Provide an interface for creating families of related or dependent
 objects without specifying their concrete classes.

 ## Explanation
+
 Real world example

 > To create a kingdom we need objects with common theme. Elven kingdom needs an Elven king, Elven castle and Elven army whereas Orcish kingdom needs an Orcish king, Orcish castle and Orcish army. There is a dependency between the objects in the kingdom.
@ -36,9 +39,11 @@ Translating the kingdom example above. First of all we have some interfaces and
 public interface Castle {
  String getDescription();
 }
+
 public interface King {
  String getDescription();
 }
+
 public interface Army {
  String getDescription();
 }
@ -66,7 +71,7 @@ public class ElfArmy implements Army {
  }
 }

-// Orcish implementations similarly...
+// Orcish implementations similarly -> ...

 ```

@ -112,9 +117,17 @@ var castle = factory.createCastle();
 var king = factory.createKing();
 var army = factory.createArmy();

-castle.getDescription();  // Output: This is the Elven castle!
-king.getDescription(); // Output: This is the Elven king!
-army.getDescription(); // Output: This is the Elven Army!
+castle.getDescription();
+king.getDescription();
+army.getDescription();
+```
+
+Program output:
+
+```java
+This is the Elven castle!
+This is the Elven king!
+This is the Elven Army!
 ```

 Now, we can design a factory for our different kingdom factories. In this example, we created FactoryMaker, responsible for returning an instance of either ElfKingdomFactory or OrcKingdomFactory.  
@ -156,37 +169,39 @@ public static void main(String[] args) {
 ```

 ## Class diagram
+
 ![alt text](./etc/abstract-factory.urm.png "Abstract Factory class diagram")


 ## Applicability
+
 Use the Abstract Factory pattern when

-* a system should be independent of how its products are created, composed and represented
-* a system should be configured with one of multiple families of products
-* a family of related product objects is designed to be used together, and you need to enforce this constraint
-* you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
-* the lifetime of the dependency is conceptually shorter than the lifetime of the consumer.
-*	you need a run-time value to construct a particular dependency
-*	you want to decide which product to call from a family at runtime.
-*	you need to supply one or more parameters only known at run-time before you can resolve a dependency.
-* when you need consistency among products
-* you don’t want to change existing code when adding new products or families of products to the program.
+* The system should be independent of how its products are created, composed and represented
+* The system should be configured with one of multiple families of products
+* The family of related product objects is designed to be used together, and you need to enforce this constraint
+* You want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
+* The lifetime of the dependency is conceptually shorter than the lifetime of the consumer.
+* You need a run-time value to construct a particular dependency
+* You want to decide which product to call from a family at runtime.
+* You need to supply one or more parameters only known at run-time before you can resolve a dependency.
+* When you need consistency among products
+* You don’t want to change existing code when adding new products or families of products to the program.

 ## Use Cases:	

-*	Selecting to call the appropriate implementation of FileSystemAcmeService or DatabaseAcmeService or NetworkAcmeService at runtime.
-*	Unit test case writing becomes much easier
+* Selecting to call the appropriate implementation of FileSystemAcmeService or DatabaseAcmeService or NetworkAcmeService at runtime.
+* Unit test case writing becomes much easier
 * UI tools for different OS

 ## Consequences:

-*	Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
+* Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
 * While the pattern is great when creating predefined objects, adding the new ones might be challenging.
-* The code may become more complicated than it should be, since a lot of new interfaces and classes are introduced along with the pattern.
-
+* The code becomes more complicated than it should be, since a lot of new interfaces and classes are introduced along with the pattern.

 ## Tutorial
+
 * [Abstract Factory Pattern Tutorial](https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java) 


--- a/abstract-factory/src/main/java/com/iluwatar/abstractfactory/module-info.java
+++ b/abstract-factory/src/main/java/com/iluwatar/abstractfactory/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.abstractfactory {
-	requires org.slf4j;
-}
--- a/abstract-factory/src/test/java/com/iluwatar/abstractfactory/AbstractFactoryTest.java
+++ b/abstract-factory/src/test/java/com/iluwatar/abstractfactory/AbstractFactoryTest.java
@ -36,7 +36,7 @@ import org.junit.jupiter.api.Test;
 */
 public class AbstractFactoryTest {

-  private App app = new App();
+  private final App app = new App();
  private KingdomFactory elfFactory;
  private KingdomFactory orcFactory;

--- a/acyclic-visitor/README.md
+++ b/acyclic-visitor/README.md
@ -9,12 +9,126 @@ tags:
 ---

 ## Intent
-Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating the troublesome dependency cycles that are inherent to the GOF VISITOR Pattern.
+
+Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating 
+the troublesome dependency cycles that are inherent to the GoF Visitor Pattern.
+
+## Explanation
+
+Real world example
+
+> We have a hierarchy of modem classes. The modems in this hierarchy need to be visited by an external algorithm based 
+> on filtering criteria (is it Unix or DOS compatible modem). 
+
+In plain words
+
+> Acyclic Visitor allows functions to be added to existing class hierarchies without modifying the hierarchies.
+
+[WikiWikiWeb](https://wiki.c2.com/?AcyclicVisitor) says
+
+> The Acyclic Visitor pattern allows new functions to be added to existing class hierarchies without affecting those 
+> hierarchies, and without creating the dependency cycles that are inherent to the GangOfFour VisitorPattern.
+
+**Programmatic Example**
+
+Here's the `Modem` hierarchy.
+
+```java
+public abstract class Modem {
+  public abstract void accept(ModemVisitor modemVisitor);
+}
+
+public class Zoom extends Modem {
+  ...
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof ZoomVisitor) {
+      ((ZoomVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only ZoomVisitor is allowed to visit Zoom modem");
+    }
+  }
+}
+
+public class Hayes extends Modem {
+  ...
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof HayesVisitor) {
+      ((HayesVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only HayesVisitor is allowed to visit Hayes modem");
+    }
+  }
+}
+```
+
+Next we introduce the `ModemVisitor` hierarchy.
+
+```java
+public interface ModemVisitor {
+}
+
+public interface HayesVisitor extends ModemVisitor {
+  void visit(Hayes hayes);
+}
+
+public interface ZoomVisitor extends ModemVisitor {
+  void visit(Zoom zoom);
+}
+
+public interface AllModemVisitor extends ZoomVisitor, HayesVisitor {
+}
+
+public class ConfigureForDosVisitor implements AllModemVisitor {
+  ...
+  @Override
+  public void visit(Hayes hayes) {
+    LOGGER.info(hayes + " used with Dos configurator.");
+  }
+  @Override
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Dos configurator.");
+  }
+}
+
+public class ConfigureForUnixVisitor implements ZoomVisitor {
+  ...
+  @Override
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Unix configurator.");
+  }
+}
+```
+
+Finally here are the visitors in action.
+
+```java
+    var conUnix = new ConfigureForUnixVisitor();
+    var conDos = new ConfigureForDosVisitor();
+    var zoom = new Zoom();
+    var hayes = new Hayes();
+    hayes.accept(conDos);
+    zoom.accept(conDos);
+    hayes.accept(conUnix);
+    zoom.accept(conUnix);   
+```
+
+Program output:
+
+```
+    // Hayes modem used with Dos configurator.
+    // Zoom modem used with Dos configurator.
+    // Only HayesVisitor is allowed to visit Hayes modem
+    // Zoom modem used with Unix configurator.
+```

 ## Class diagram
+
 ![alt text](./etc/acyclic-visitor.png "Acyclic Visitor")

 ## Applicability
+
 This pattern can be used:

 * When you need to add a new function to an existing hierarchy without the need to alter or affect that hierarchy.
@ -24,6 +138,7 @@ This pattern can be used:
 * When the recompilation, relinking, retesting or redistribution of the derivatives of Element is very expensive.

 ## Consequences
+
 The good:

 * No dependency cycles between class hierarchies.
@ -32,11 +147,14 @@ The good:

 The bad:

-* Violates the principle of least surprise or Liskov's Substitution principle by showing that it can accept all visitors but actually only being interested in particular visitors.
+* Violates [Liskov's Substitution Principle](https://java-design-patterns.com/principles/#liskov-substitution-principle) by showing that it can accept all visitors but actually only being interested in particular visitors.
 * Parallel hierarchy of visitors has to be created for all members in visitable class hierarchy.

 ## Related patterns
-* [Visitor Pattern](../visitor/)
+
+* [Visitor Pattern](https://java-design-patterns.com/patterns/visitor/)

 ## Credits
-* [Acyclic Visitor](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)
+
+* [Acyclic Visitor by Robert C. Martin](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)
+* [Acyclic Visitor in WikiWikiWeb](https://wiki.c2.com/?AcyclicVisitor)
--- a/acyclic-visitor/etc/Acyclic
+++ b/acyclic-visitor/etc/Acyclic
@ -1,115 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<class-diagram version="1.2.2" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
-  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
-  <interface id="1" language="java" name="com.iluwatar.acyclicvisitor.ModemVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ModemVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="860" y="67"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <class id="2" language="java" name="com.iluwatar.acyclicvisitor.Modem" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Modem.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="327" y="77"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="3" language="java" name="com.iluwatar.acyclicvisitor.ConfigureForUnixVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForUnixVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="124" width="196" x="647" y="225"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="4" language="java" name="com.iluwatar.acyclicvisitor.Zoom" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Zoom.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="203" y="305"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <interface id="5" language="java" name="com.iluwatar.acyclicvisitor.HayesVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/HayesVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="1019" y="468"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <interface id="6" language="java" name="com.iluwatar.acyclicvisitor.ZoomVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ZoomVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="758" y="467"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <class id="7" language="java" name="com.iluwatar.acyclicvisitor.Hayes" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Hayes.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="479" y="307"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="8" language="java" name="com.iluwatar.acyclicvisitor.ConfigureForDosVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="142" width="192" x="883" y="225"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <generalization id="9">    
-    <end type="SOURCE" refId="7"/>    
-    <end type="TARGET" refId="2"/>  
-  </generalization>  
-  <realization id="10">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="6"/>  
-  </realization>  
-  <realization id="11">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="5"/>  
-  </realization>  
-  <realization id="12">    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="6"/>  
-  </realization>  
-  <realization id="13">    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <realization id="14">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <generalization id="15">    
-    <end type="SOURCE" refId="4"/>    
-    <end type="TARGET" refId="2"/>  
-  </generalization>  
-  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-    sort-features="false" accessors="true" visibility="true">    
-    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
-    <operations public="true" package="true" protected="true" private="true" static="true"/>  
-  </classifier-display>  
-  <association-display labels="true" multiplicity="true"/>
-</class-diagram>
--- a/acyclic-visitor/etc/acyclic-visitor.png
+++ b/acyclic-visitor/etc/acyclic-visitor.png
--- a/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/module-info.java
+++ b/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.acyclicvisitor {
-	requires org.slf4j;
-}
--- a/acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitorTest.java
+++ b/acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitorTest.java
@ -37,7 +37,7 @@ import uk.org.lidalia.slf4jtest.TestLoggerFactory;
 */
 public class ConfigureForDosVisitorTest {

-  private TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
+  private final TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
  
  @Test
  public void testVisitForZoom() {    
--- a/adapter/README.md
+++ b/adapter/README.md
@ -56,7 +56,7 @@ And captain expects an implementation of `RowingBoat` interface to be able to mo
 ```java
 public class Captain {

-  private RowingBoat rowingBoat;
+  private final RowingBoat rowingBoat;
  // default constructor and setter for rowingBoat
  public Captain(RowingBoat rowingBoat) {
    this.rowingBoat = rowingBoat;
@ -75,7 +75,7 @@ public class FishingBoatAdapter implements RowingBoat {

  private static final Logger LOGGER = LoggerFactory.getLogger(FishingBoatAdapter.class);

-  private FishingBoat boat;
+  private final FishingBoat boat;

  public FishingBoatAdapter() {
    boat = new FishingBoat();
--- a/adapter/src/main/java/com/iluwatar/adapter/FishingBoatAdapter.java
+++ b/adapter/src/main/java/com/iluwatar/adapter/FishingBoatAdapter.java
@ -29,7 +29,7 @@ package com.iluwatar.adapter;
 */
 public class FishingBoatAdapter implements RowingBoat {

-  private FishingBoat boat;
+  private final FishingBoat boat;

  public FishingBoatAdapter() {
    boat = new FishingBoat();
--- a/ambassador/src/test/java/com/iluwatar/ambassador/RemoteServiceTest.java
+++ b/ambassador/src/test/java/com/iluwatar/ambassador/RemoteServiceTest.java
@ -48,7 +48,7 @@ class RemoteServiceTest {
  }

  private static class StaticRandomProvider implements RandomProvider {
-    private double value;
+    private final double value;

    StaticRandomProvider(double value) {
      this.value = value;
--- a/arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAAATest.java
+++ b/arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAAATest.java
@ -60,7 +60,7 @@ public class CashAAATest {
    //Act
    cash.plus(4);
    //Assert
-    assertEquals(cash.count(), 7);
+    assertEquals(7, cash.count());
  }

  @Test
@ -71,7 +71,7 @@ public class CashAAATest {
    var result = cash.minus(5);
    //Assert
    assertTrue(result);
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
  }

  @Test
@ -82,7 +82,7 @@ public class CashAAATest {
    var result = cash.minus(6);
    //Assert
    assertFalse(result);
-    assertEquals(cash.count(), 1);
+    assertEquals(1, cash.count());
  }

  @Test
@ -94,6 +94,6 @@ public class CashAAATest {
    var result = cash.minus(3);
    //Assert
    assertTrue(result);
-    assertEquals(cash.count(), 8);
+    assertEquals(8, cash.count());
  }
 }
--- a/arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAntiAAATest.java
+++ b/arrange-act-assert/src/test/java/com/iluwatar/arrangeactassert/CashAntiAAATest.java
@ -44,16 +44,16 @@ public class CashAntiAAATest {
    var cash = new Cash(3);
    //test plus
    cash.plus(4);
-    assertEquals(cash.count(), 7);
+    assertEquals(7, cash.count());
    //test minus
    cash = new Cash(8);
    assertTrue(cash.minus(5));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
    assertFalse(cash.minus(6));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
    //test update
    cash.plus(5);
    assertTrue(cash.minus(5));
-    assertEquals(cash.count(), 3);
+    assertEquals(3, cash.count());
  }
 }
--- a/async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/ThreadAsyncExecutor.java
+++ b/async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/ThreadAsyncExecutor.java
@ -100,7 +100,7 @@ public class ThreadAsyncExecutor implements AsyncExecutor {
    void setValue(T value) {
      this.value = value;
      this.state = COMPLETED;
-      this.callback.ifPresent(ac -> ac.onComplete(value, Optional.<Exception>empty()));
+      this.callback.ifPresent(ac -> ac.onComplete(value, Optional.empty()));
      synchronized (lock) {
        lock.notifyAll();
      }
--- a/business-delegate/src/main/java/com/iluwatar/business/delegate/Client.java
+++ b/business-delegate/src/main/java/com/iluwatar/business/delegate/Client.java
@ -28,7 +28,7 @@ package com.iluwatar.business.delegate;
 */
 public class Client {

-  private BusinessDelegate businessDelegate;
+  private final BusinessDelegate businessDelegate;

  public Client(BusinessDelegate businessDelegate) {
    this.businessDelegate = businessDelegate;
--- a/business-delegate/src/main/java/com/iluwatar/business/delegate/ServiceType.java
+++ b/business-delegate/src/main/java/com/iluwatar/business/delegate/ServiceType.java
@ -28,5 +28,5 @@ package com.iluwatar.business.delegate;
 */
 public enum ServiceType {

-  EJB, JMS;
+  EJB, JMS
 }
--- a/business-delegate/src/main/java/com/iluwatar/business/delegate/module-info.java
+++ b/business-delegate/src/main/java/com/iluwatar/business/delegate/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.business.delegate {
-	requires org.slf4j;
-}
--- a/bytecode/src/main/java/com/iluwatar/bytecode/VirtualMachine.java
+++ b/bytecode/src/main/java/com/iluwatar/bytecode/VirtualMachine.java
@ -30,9 +30,9 @@ import java.util.Stack;
 */
 public class VirtualMachine {

-  private Stack<Integer> stack = new Stack<>();
+  private final Stack<Integer> stack = new Stack<>();

-  private Wizard[] wizards = new Wizard[2];
+  private final Wizard[] wizards = new Wizard[2];

  /**
   * Constructor.
--- a/bytecode/src/test/java/com/iluwatar/bytecode/VirtualMachineTest.java
+++ b/bytecode/src/test/java/com/iluwatar/bytecode/VirtualMachineTest.java
@ -104,7 +104,7 @@ public class VirtualMachineTest {
    bytecode[2] = LITERAL.getIntValue();
    bytecode[3] = 50;                        // health amount
    bytecode[4] = SET_HEALTH.getIntValue();
-    bytecode[5] = LITERAL.getIntValue();;
+    bytecode[5] = LITERAL.getIntValue();
    bytecode[6] = wizardNumber;
    bytecode[7] = GET_HEALTH.getIntValue();

--- a/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
+++ b/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
@ -29,7 +29,7 @@ package com.iluwatar.caching;
 public enum CachingPolicy {
  THROUGH("through"), AROUND("around"), BEHIND("behind"), ASIDE("aside");

-  private String policy;
+  private final String policy;

  CachingPolicy(String policy) {
    this.policy = policy;
--- a/callback/src/main/java/com/iluwatar/callback/module-info.java
+++ b/callback/src/main/java/com/iluwatar/callback/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.callback {
-	requires org.slf4j;
-}
--- a/chain/README.md
+++ b/chain/README.md
@ -65,7 +65,7 @@ Then the request handler hierarchy
 ```java
 public abstract class RequestHandler {
  private static final Logger LOGGER = LoggerFactory.getLogger(RequestHandler.class);
-  private RequestHandler next;
+  private final RequestHandler next;

  public RequestHandler(RequestHandler next) {
    this.next = next;
--- a/chain/src/main/java/com/iluwatar/chain/RequestHandler.java
+++ b/chain/src/main/java/com/iluwatar/chain/RequestHandler.java
@ -33,7 +33,7 @@ public abstract class RequestHandler {

  private static final Logger LOGGER = LoggerFactory.getLogger(RequestHandler.class);

-  private RequestHandler next;
+  private final RequestHandler next;

  public RequestHandler(RequestHandler next) {
    this.next = next;
--- a/chain/src/main/java/com/iluwatar/chain/module-info.java
+++ b/chain/src/main/java/com/iluwatar/chain/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.chain {
-	requires org.slf4j;
-}
--- a/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java
+++ b/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java
@ -87,10 +87,7 @@ public class Car {
    } else if (!model.equals(other.model)) {
      return false;
    }
-    if (year != other.year) {
-      return false;
-    }
-    return true;
+    return year == other.year;
  }

  public String getMake() {
--- a/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Person.java
+++ b/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Person.java
@ -29,7 +29,7 @@ import java.util.List;
 * A Person class that has the list of cars that the person owns and use.
 */
 public class Person {
-  private List<Car> cars;
+  private final List<Car> cars;

  /**
   * Constructor to create an instance of person.
--- a/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/module-info.java
+++ b/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.collectionpipeline {
-	requires org.slf4j;
-}
--- a/collection-pipeline/src/test/java/com/iluwatar/collectionpipeline/AppTest.java
+++ b/collection-pipeline/src/test/java/com/iluwatar/collectionpipeline/AppTest.java
@ -37,7 +37,7 @@ import org.slf4j.LoggerFactory;
 public class AppTest {
  private static final Logger LOGGER = LoggerFactory.getLogger(AppTest.class);

-  private List<Car> cars = CarFactory.createCars();
+  private final List<Car> cars = CarFactory.createCars();

  @Test
  public void testGetModelsAfter2000UsingFor() {
--- a/command/README.md
+++ b/command/README.md
@ -36,8 +36,8 @@ public class Wizard {

  private static final Logger LOGGER = LoggerFactory.getLogger(Wizard.class);

-  private Deque<Command> undoStack = new LinkedList<>();
-  private Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Command> undoStack = new LinkedList<>();
+  private final Deque<Command> redoStack = new LinkedList<>();

  public Wizard() {}

--- a/command/src/main/java/com/iluwatar/command/Size.java
+++ b/command/src/main/java/com/iluwatar/command/Size.java
@ -1,43 +1,43 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.command;
-
-/**
- * Enumeration for target size.
- */
-public enum Size {
-
-  SMALL("small"), NORMAL("normal");
-
-  private String title;
-
-  Size(String title) {
-    this.title = title;
-  }
-
-  @Override
-  public String toString() {
-    return title;
-  }
-}
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.command;
+
+/**
+ * Enumeration for target size.
+ */
+public enum Size {
+
+  SMALL("small"), NORMAL("normal");
+
+  private final String title;
+
+  Size(String title) {
+    this.title = title;
+  }
+
+  @Override
+  public String toString() {
+    return title;
+  }
+}
--- a/command/src/main/java/com/iluwatar/command/Visibility.java
+++ b/command/src/main/java/com/iluwatar/command/Visibility.java
@ -1,43 +1,43 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.command;
-
-/**
- * Enumeration for target visibility.
- */
-public enum Visibility {
-
-  VISIBLE("visible"), INVISIBLE("invisible");
-
-  private String title;
-
-  Visibility(String title) {
-    this.title = title;
-  }
-
-  @Override
-  public String toString() {
-    return title;
-  }
-}
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.command;
+
+/**
+ * Enumeration for target visibility.
+ */
+public enum Visibility {
+
+  VISIBLE("visible"), INVISIBLE("invisible");
+
+  private final String title;
+
+  Visibility(String title) {
+    this.title = title;
+  }
+
+  @Override
+  public String toString() {
+    return title;
+  }
+}
--- a/command/src/main/java/com/iluwatar/command/Wizard.java
+++ b/command/src/main/java/com/iluwatar/command/Wizard.java
@ -35,8 +35,8 @@ public class Wizard {

  private static final Logger LOGGER = LoggerFactory.getLogger(Wizard.class);

-  private Deque<Command> undoStack = new LinkedList<>();
-  private Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Command> undoStack = new LinkedList<>();
+  private final Deque<Command> redoStack = new LinkedList<>();

  public Wizard() {
    // comment to ignore sonar issue: LEVEL critical
--- a/command/src/main/java/com/iluwatar/command/module-info.java
+++ b/command/src/main/java/com/iluwatar/command/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.command {
-	requires org.slf4j;
-}
--- a/commander/src/main/java/com/iluwatar/commander/employeehandle/EmployeeDatabase.java
+++ b/commander/src/main/java/com/iluwatar/commander/employeehandle/EmployeeDatabase.java
@ -33,7 +33,7 @@ import java.util.Hashtable;
 */

 public class EmployeeDatabase extends Database<Order> {
-  private Hashtable<String, Order> data;
+  private final Hashtable<String, Order> data;

  public EmployeeDatabase() {
    this.data = new Hashtable<>();
--- a/commander/src/main/java/com/iluwatar/commander/messagingservice/MessagingDatabase.java
+++ b/commander/src/main/java/com/iluwatar/commander/messagingservice/MessagingDatabase.java
@ -33,7 +33,7 @@ import java.util.Hashtable;
 */

 public class MessagingDatabase extends Database<MessageRequest> {
-  private Hashtable<String, MessageRequest> data;
+  private final Hashtable<String, MessageRequest> data;

  public MessagingDatabase() {
    this.data = new Hashtable<>();
--- a/commander/src/main/java/com/iluwatar/commander/paymentservice/PaymentDatabase.java
+++ b/commander/src/main/java/com/iluwatar/commander/paymentservice/PaymentDatabase.java
@ -34,7 +34,7 @@ import java.util.Hashtable;

 public class PaymentDatabase extends Database<PaymentRequest> {

-  private Hashtable<String, PaymentRequest> data;
+  private final Hashtable<String, PaymentRequest> data;

  public PaymentDatabase() {
    this.data = new Hashtable<>();
--- a/commander/src/main/java/com/iluwatar/commander/queue/QueueDatabase.java
+++ b/commander/src/main/java/com/iluwatar/commander/queue/QueueDatabase.java
@ -35,7 +35,7 @@ import java.util.List;

 public class QueueDatabase extends Database<QueueTask> {

-  private Queue<QueueTask> data;
+  private final Queue<QueueTask> data;
  public List<Exception> exceptionsList;

  public QueueDatabase(Exception... exc) {
--- a/commander/src/main/java/com/iluwatar/commander/shippingservice/ShippingDatabase.java
+++ b/commander/src/main/java/com/iluwatar/commander/shippingservice/ShippingDatabase.java
@ -34,7 +34,7 @@ import java.util.Hashtable;

 public class ShippingDatabase extends Database<ShippingRequest> {

-  private Hashtable<String, ShippingRequest> data;
+  private final Hashtable<String, ShippingRequest> data;

  public ShippingDatabase() {
    this.data = new Hashtable<>();
--- a/composite/README.md
+++ b/composite/README.md
@ -34,7 +34,7 @@ Taking our sentence example from above. Here we have the base class and differen
 ```java
 public abstract class LetterComposite {

-  private List<LetterComposite> children = new ArrayList<>();
+  private final List<LetterComposite> children = new ArrayList<>();

  public void add(LetterComposite letter) {
    children.add(letter);
@ -59,7 +59,7 @@ public abstract class LetterComposite {

 public class Letter extends LetterComposite {

-  private char character;
+  private final char character;

  public Letter(char c) {
    this.character = c;
--- a/composite/src/main/java/com/iluwatar/composite/Letter.java
+++ b/composite/src/main/java/com/iluwatar/composite/Letter.java
@ -28,7 +28,7 @@ package com.iluwatar.composite;
 */
 public class Letter extends LetterComposite {

-  private char character;
+  private final char character;

  public Letter(char c) {
    this.character = c;
--- a/composite/src/main/java/com/iluwatar/composite/LetterComposite.java
+++ b/composite/src/main/java/com/iluwatar/composite/LetterComposite.java
@ -1,58 +1,58 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.composite;
-
-import java.util.ArrayList;
-import java.util.List;
-
-/**
- * Composite interface.
- */
-public abstract class LetterComposite {
-
-  private List<LetterComposite> children = new ArrayList<>();
-
-  public void add(LetterComposite letter) {
-    children.add(letter);
-  }
-
-  public int count() {
-    return children.size();
-  }
-
-  protected void printThisBefore() {
-  }
-
-  protected void printThisAfter() {
-  }
-
-  /**
-   * Print.
-   */
-  public void print() {
-    printThisBefore();
-    children.forEach(LetterComposite::print);
-    printThisAfter();
-  }
-}
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.composite;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Composite interface.
+ */
+public abstract class LetterComposite {
+
+  private final List<LetterComposite> children = new ArrayList<>();
+
+  public void add(LetterComposite letter) {
+    children.add(letter);
+  }
+
+  public int count() {
+    return children.size();
+  }
+
+  protected void printThisBefore() {
+  }
+
+  protected void printThisAfter() {
+  }
+
+  /**
+   * Print.
+   */
+  public void print() {
+    printThisBefore();
+    children.forEach(LetterComposite::print);
+    printThisAfter();
+  }
+}
--- a/composite/src/main/java/com/iluwatar/composite/module-info.java
+++ b/composite/src/main/java/com/iluwatar/composite/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.composite {
-	requires org.slf4j;
-}
--- a/converter/src/main/java/com/iluwatar/converter/User.java
+++ b/converter/src/main/java/com/iluwatar/converter/User.java
@ -29,10 +29,10 @@ import java.util.Objects;
 * User class.
 */
 public class User {
-  private String firstName;
-  private String lastName;
-  private boolean isActive;
-  private String userId;
+  private final String firstName;
+  private final String lastName;
+  private final boolean isActive;
+  private final String userId;

  /**
   * Constructor.
--- a/converter/src/main/java/com/iluwatar/converter/UserDto.java
+++ b/converter/src/main/java/com/iluwatar/converter/UserDto.java
@ -30,10 +30,10 @@ import java.util.Objects;
 */
 public class UserDto {

-  private String firstName;
-  private String lastName;
-  private boolean isActive;
-  private String email;
+  private final String firstName;
+  private final String lastName;
+  private final boolean isActive;
+  private final String email;

  /**
   * Constructor.
--- a/converter/src/main/java/com/iluwatar/converter/module-info.java
+++ b/converter/src/main/java/com/iluwatar/converter/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.converter {
-	requires org.slf4j;
-}
--- a/converter/src/test/java/com/iluwatar/converter/ConverterTest.java
+++ b/converter/src/test/java/com/iluwatar/converter/ConverterTest.java
@ -34,7 +34,7 @@ import org.junit.jupiter.api.Test;
 */
 public class ConverterTest {

-  private UserConverter userConverter = new UserConverter();
+  private final UserConverter userConverter = new UserConverter();

  /**
   * Tests whether a converter created of opposite functions holds equality as a bijection.
--- a/cqrs/src/main/java/com/iluwatar/cqrs/commandes/CommandServiceImpl.java
+++ b/cqrs/src/main/java/com/iluwatar/cqrs/commandes/CommandServiceImpl.java
@ -34,7 +34,7 @@ import org.hibernate.SessionFactory;
 */
 public class CommandServiceImpl implements ICommandService {

-  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+  private final SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

  private Author getAuthorByUsername(String username) {
    Author author;
--- a/cqrs/src/main/java/com/iluwatar/cqrs/queries/QueryServiceImpl.java
+++ b/cqrs/src/main/java/com/iluwatar/cqrs/queries/QueryServiceImpl.java
@ -38,7 +38,7 @@ import org.hibernate.transform.Transformers;
 */
 public class QueryServiceImpl implements IQueryService {

-  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
+  private final SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

  @Override
  public Author getAuthorByUsername(String username) {
--- a/dao/README.md
+++ b/dao/README.md
@ -112,7 +112,7 @@ public interface CustomerDao {

 public class InMemoryCustomerDao implements CustomerDao {

-  private Map<Integer, Customer> idToCustomer = new HashMap<>();
+  private final Map<Integer, Customer> idToCustomer = new HashMap<>();

  @Override
  public Stream<Customer> getAll() {
--- a/dao/src/main/java/com/iluwatar/dao/App.java
+++ b/dao/src/main/java/com/iluwatar/dao/App.java
@ -44,7 +44,7 @@ import org.slf4j.LoggerFactory;
 */
 public class App {
  private static final String DB_URL = "jdbc:h2:~/dao";
-  private static Logger log = LoggerFactory.getLogger(App.class);
+  private static final Logger log = LoggerFactory.getLogger(App.class);
  private static final String ALL_CUSTOMERS = "customerDao.getAllCustomers(): ";

  /**
--- a/dao/src/main/java/com/iluwatar/dao/InMemoryCustomerDao.java
+++ b/dao/src/main/java/com/iluwatar/dao/InMemoryCustomerDao.java
@ -36,7 +36,7 @@ import java.util.stream.Stream;
 */
 public class InMemoryCustomerDao implements CustomerDao {

-  private Map<Integer, Customer> idToCustomer = new HashMap<>();
+  private final Map<Integer, Customer> idToCustomer = new HashMap<>();

  /**
   * An eagerly evaluated stream of customers stored in memory.
--- a/dao/src/main/java/com/iluwatar/dao/module-info.java
+++ b/dao/src/main/java/com/iluwatar/dao/module-info.java
@ -1,29 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.dao {
-	requires org.slf4j;
-	requires java.sql;
-	requires h2;
-	requires java.naming;
-}
--- a/dao/src/test/java/com/iluwatar/dao/DbCustomerDaoTest.java
+++ b/dao/src/test/java/com/iluwatar/dao/DbCustomerDaoTest.java
@ -50,7 +50,7 @@ public class DbCustomerDaoTest {

  private static final String DB_URL = "jdbc:h2:~/dao";
  private DbCustomerDao dao;
-  private Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
+  private final Customer existingCustomer = new Customer(1, "Freddy", "Krueger");

  /**
   * Creates customers schema.
--- a/data-bus/src/main/java/com/iluwatar/databus/members/MessageCollectorMember.java
+++ b/data-bus/src/main/java/com/iluwatar/databus/members/MessageCollectorMember.java
@ -41,7 +41,7 @@ public class MessageCollectorMember implements Member {

  private final String name;

-  private List<String> messages = new ArrayList<>();
+  private final List<String> messages = new ArrayList<>();

  public MessageCollectorMember(String name) {
    this.name = name;
--- a/data-mapper/src/main/java/com/iluwatar/datamapper/App.java
+++ b/data-mapper/src/main/java/com/iluwatar/datamapper/App.java
@ -1,83 +1,83 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.datamapper;
-
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
- * database. Its responsibility is to transfer data between the two and also to isolate them from
- * each other. With Data Mapper the in-memory objects needn't know even that there's a database
- * present; they need no SQL interface code, and certainly no knowledge of the database schema. (The
- * database schema is always ignorant of the objects that use it.) Since it's a form of Mapper ,
- * Data Mapper itself is even unknown to the domain layer.
- *
- * <p>The below example demonstrates basic CRUD operations: Create, Read, Update, and Delete.
- */
-public final class App {
-
-  private static Logger log = LoggerFactory.getLogger(App.class);
-  private static final String STUDENT_STRING = "App.main(), student : ";
-
-
-  /**
-   * Program entry point.
-   *
-   * @param args command line args.
-   */
-  public static void main(final String... args) {
-
-    /* Create new data mapper for type 'first' */
-    final var mapper = new StudentDataMapperImpl();
-
-    /* Create new student */
-    var student = new Student(1, "Adam", 'A');
-
-    /* Add student in respectibe store */
-    mapper.insert(student);
-
-    log.debug(STUDENT_STRING + student + ", is inserted");
-
-    /* Find this student */
-    final var studentToBeFound = mapper.find(student.getStudentId());
-
-    log.debug(STUDENT_STRING + studentToBeFound + ", is searched");
-
-    /* Update existing student object */
-    student = new Student(student.getStudentId(), "AdamUpdated", 'A');
-
-    /* Update student in respectibe db */
-    mapper.update(student);
-
-    log.debug(STUDENT_STRING + student + ", is updated");
-    log.debug(STUDENT_STRING + student + ", is going to be deleted");
-
-    /* Delete student in db */
-    mapper.delete(student);
-  }
-
-  private App() {
-  }
-}
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.datamapper;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
+ * database. Its responsibility is to transfer data between the two and also to isolate them from
+ * each other. With Data Mapper the in-memory objects needn't know even that there's a database
+ * present; they need no SQL interface code, and certainly no knowledge of the database schema. (The
+ * database schema is always ignorant of the objects that use it.) Since it's a form of Mapper ,
+ * Data Mapper itself is even unknown to the domain layer.
+ *
+ * <p>The below example demonstrates basic CRUD operations: Create, Read, Update, and Delete.
+ */
+public final class App {
+
+  private static final Logger log = LoggerFactory.getLogger(App.class);
+  private static final String STUDENT_STRING = "App.main(), student : ";
+
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line args.
+   */
+  public static void main(final String... args) {
+
+    /* Create new data mapper for type 'first' */
+    final var mapper = new StudentDataMapperImpl();
+
+    /* Create new student */
+    var student = new Student(1, "Adam", 'A');
+
+    /* Add student in respectibe store */
+    mapper.insert(student);
+
+    log.debug(STUDENT_STRING + student + ", is inserted");
+
+    /* Find this student */
+    final var studentToBeFound = mapper.find(student.getStudentId());
+
+    log.debug(STUDENT_STRING + studentToBeFound + ", is searched");
+
+    /* Update existing student object */
+    student = new Student(student.getStudentId(), "AdamUpdated", 'A');
+
+    /* Update student in respectibe db */
+    mapper.update(student);
+
+    log.debug(STUDENT_STRING + student + ", is updated");
+    log.debug(STUDENT_STRING + student + ", is going to be deleted");
+
+    /* Delete student in db */
+    mapper.delete(student);
+  }
+
+  private App() {
+  }
+}
--- a/data-mapper/src/main/java/com/iluwatar/datamapper/StudentDataMapperImpl.java
+++ b/data-mapper/src/main/java/com/iluwatar/datamapper/StudentDataMapperImpl.java
@ -33,7 +33,7 @@ import java.util.Optional;
 public final class StudentDataMapperImpl implements StudentDataMapper {

  /* Note: Normally this would be in the form of an actual database */
-  private List<Student> students = new ArrayList<>();
+  private final List<Student> students = new ArrayList<>();

  @Override
  public Optional<Student> find(int studentId) {
--- a/data-mapper/src/main/java/com/iluwatar/datamapper/module-info.java
+++ b/data-mapper/src/main/java/com/iluwatar/datamapper/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.datamapper {
-	requires org.slf4j;
-}
--- a/data-transfer-object/README.md
+++ b/data-transfer-object/README.md
@ -64,7 +64,7 @@ Customer resource class acts as the server for customer information.

 ```java
 public class CustomerResource {
-  private List<CustomerDto> customers;
+  private final List<CustomerDto> customers;

  public CustomerResource(List<CustomerDto> customers) {
    this.customers = customers;
--- a/data-transfer-object/src/main/java/com/iluwatar/datatransfer/CustomerResource.java
+++ b/data-transfer-object/src/main/java/com/iluwatar/datatransfer/CustomerResource.java
@ -30,7 +30,7 @@ import java.util.List;
 * has all customer details.
 */
 public class CustomerResource {
-  private List<CustomerDto> customers;
+  private final List<CustomerDto> customers;

  /**
   * Initialise resource with existing customers.
--- a/data-transfer-object/src/main/java/com/iluwatar/datatransfer/module-info.java
+++ b/data-transfer-object/src/main/java/com/iluwatar/datatransfer/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.datatransfer {
-	requires org.slf4j;
-}
--- a/decorator/README.md
+++ b/decorator/README.md
@ -70,7 +70,7 @@ public class ClubbedTroll implements Troll {

  private static final Logger LOGGER = LoggerFactory.getLogger(ClubbedTroll.class);

-  private Troll decorated;
+  private final Troll decorated;

  public ClubbedTroll(Troll decorated) {
    this.decorated = decorated;
--- a/decorator/src/main/java/com/iluwatar/decorator/ClubbedTroll.java
+++ b/decorator/src/main/java/com/iluwatar/decorator/ClubbedTroll.java
@ -33,7 +33,7 @@ public class ClubbedTroll implements Troll {

  private static final Logger LOGGER = LoggerFactory.getLogger(ClubbedTroll.class);

-  private Troll decorated;
+  private final Troll decorated;

  public ClubbedTroll(Troll decorated) {
    this.decorated = decorated;
--- a/decorator/src/main/java/com/iluwatar/decorator/module-info.java
+++ b/decorator/src/main/java/com/iluwatar/decorator/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.decorator {
-	requires org.slf4j;
-}
--- a/decorator/src/test/java/com/iluwatar/decorator/SimpleTrollTest.java
+++ b/decorator/src/test/java/com/iluwatar/decorator/SimpleTrollTest.java
@ -68,7 +68,7 @@ public class SimpleTrollTest {

  private class InMemoryAppender extends AppenderBase<ILoggingEvent> {

-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();

    public InMemoryAppender(Class clazz) {
      ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);
--- a/delegation/src/main/java/com/iluwatar/delegation/module-info.java
+++ b/delegation/src/main/java/com/iluwatar/delegation/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.delegation {
-	requires org.slf4j;
-}
--- a/delegation/src/test/java/com/iluwatar/delegation/simple/DelegateTest.java
+++ b/delegation/src/test/java/com/iluwatar/delegation/simple/DelegateTest.java
@ -86,7 +86,7 @@ public class DelegateTest {
   */
  private class InMemoryAppender extends AppenderBase<ILoggingEvent> {

-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();

    public InMemoryAppender() {
      ((Logger) LoggerFactory.getLogger("root")).addAppender(this);
--- a/dependency-injection/README.md
+++ b/dependency-injection/README.md
@ -62,7 +62,7 @@ public interface Wizard {

 public class AdvancedWizard implements Wizard {

-  private Tobacco tobacco;
+  private final Tobacco tobacco;

  public AdvancedWizard(Tobacco tobacco) {
    this.tobacco = tobacco;
--- a/dependency-injection/src/main/java/com/iluwatar/dependency/injection/AdvancedWizard.java
+++ b/dependency-injection/src/main/java/com/iluwatar/dependency/injection/AdvancedWizard.java
@ -29,7 +29,7 @@ package com.iluwatar.dependency.injection;
 */
 public class AdvancedWizard implements Wizard {

-  private Tobacco tobacco;
+  private final Tobacco tobacco;

  public AdvancedWizard(Tobacco tobacco) {
    this.tobacco = tobacco;
--- a/dependency-injection/src/main/java/com/iluwatar/dependency/injection/GuiceWizard.java
+++ b/dependency-injection/src/main/java/com/iluwatar/dependency/injection/GuiceWizard.java
@ -31,7 +31,7 @@ import javax.inject.Inject;
 */
 public class GuiceWizard implements Wizard {

-  private Tobacco tobacco;
+  private final Tobacco tobacco;

  @Inject
  public GuiceWizard(Tobacco tobacco) {
--- a/dependency-injection/src/main/java/com/iluwatar/dependency/injection/SimpleWizard.java
+++ b/dependency-injection/src/main/java/com/iluwatar/dependency/injection/SimpleWizard.java
@ -29,7 +29,7 @@ package com.iluwatar.dependency.injection;
 */
 public class SimpleWizard implements Wizard {

-  private OldTobyTobacco tobacco = new OldTobyTobacco();
+  private final OldTobyTobacco tobacco = new OldTobyTobacco();

  public void smoke() {
    tobacco.smoke(this);
--- a/dependency-injection/src/test/java/com/iluwatar/dependency/injection/utils/InMemoryAppender.java
+++ b/dependency-injection/src/test/java/com/iluwatar/dependency/injection/utils/InMemoryAppender.java
@ -37,7 +37,7 @@ import java.util.List;
 */
 public class InMemoryAppender extends AppenderBase<ILoggingEvent> {

-  private List<ILoggingEvent> log = new LinkedList<>();
+  private final List<ILoggingEvent> log = new LinkedList<>();

  public InMemoryAppender(Class clazz) {
    ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);
--- a/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java
+++ b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java
@ -34,7 +34,7 @@ import java.util.List;
 public class World {

  private List<String> countries;
-  private DataFetcher df;
+  private final DataFetcher df;

  public World() {
    this.countries = new ArrayList<String>();
--- a/dirty-flag/src/main/java/com/iluwatar/dirtyflag/module-info.java
+++ b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.dirtyflag {
-	requires org.slf4j;
-}
--- a/double-buffer/src/main/java/com/iluwatar/doublebuffer/FrameBuffer.java
+++ b/double-buffer/src/main/java/com/iluwatar/doublebuffer/FrameBuffer.java
@ -33,7 +33,7 @@ public class FrameBuffer implements Buffer {
  public static final int WIDTH = 10;
  public static final int HEIGHT = 8;

-  private Pixel[] pixels = new Pixel[WIDTH * HEIGHT];
+  private final Pixel[] pixels = new Pixel[WIDTH * HEIGHT];

  public FrameBuffer() {
    clearAll();
--- a/double-buffer/src/main/java/com/iluwatar/doublebuffer/Pixel.java
+++ b/double-buffer/src/main/java/com/iluwatar/doublebuffer/Pixel.java
@ -31,7 +31,7 @@ public enum Pixel {
  WHITE(0),
  BLACK(1);

-  private int color;
+  private final int color;

  Pixel(int color) {
    this.color = color;
--- a/double-buffer/src/main/java/com/iluwatar/doublebuffer/Scene.java
+++ b/double-buffer/src/main/java/com/iluwatar/doublebuffer/Scene.java
@ -35,7 +35,7 @@ public class Scene {

  private static final Logger LOGGER = LoggerFactory.getLogger(Scene.class);

-  private Buffer[] frameBuffers;
+  private final Buffer[] frameBuffers;

  private int current;

--- a/double-checked-locking/src/main/java/com/iluwatar/doublechecked/locking/module-info.java
+++ b/double-checked-locking/src/main/java/com/iluwatar/doublechecked/locking/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.doublecheckedlocking {
-	requires org.slf4j;
-}
--- a/double-checked-locking/src/test/java/com/iluwatar/doublechecked/locking/InventoryTest.java
+++ b/double-checked-locking/src/test/java/com/iluwatar/doublechecked/locking/InventoryTest.java
@ -109,7 +109,7 @@ public class InventoryTest {


  private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();

    public InMemoryAppender(Class clazz) {
      ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);
--- a/double-dispatch/src/main/java/com/iluwatar/doubledispatch/Rectangle.java
+++ b/double-dispatch/src/main/java/com/iluwatar/doubledispatch/Rectangle.java
@ -28,10 +28,10 @@ package com.iluwatar.doubledispatch;
 */
 public class Rectangle {

-  private int left;
-  private int top;
-  private int right;
-  private int bottom;
+  private final int left;
+  private final int top;
+  private final int right;
+  private final int bottom;

  /**
   * Constructor.
--- a/double-dispatch/src/main/java/com/iluwatar/doubledispatch/module-info.java
+++ b/double-dispatch/src/main/java/com/iluwatar/doubledispatch/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.doubledispatch {
-	requires org.slf4j;
-}
--- a/eip-message-channel/src/main/java/com/iluwatar/eip/message/channel/module-info.java
+++ b/eip-message-channel/src/main/java/com/iluwatar/eip/message/channel/module-info.java
@ -1,27 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.eipmessagechannel {
-	requires org.slf4j;
-	requires camel.core;
-}
--- a/eip-publish-subscribe/src/main/java/com/iluwatar/eip/publish/subscribe/module-info.java
+++ b/eip-publish-subscribe/src/main/java/com/iluwatar/eip/publish/subscribe/module-info.java
@ -1,27 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.eippublishsubscribe {
-	requires org.slf4j;
-	requires camel.core;
-}
--- a/event-aggregator/src/main/java/com/iluwatar/event/aggregator/Event.java
+++ b/event-aggregator/src/main/java/com/iluwatar/event/aggregator/Event.java
@ -31,7 +31,7 @@ public enum Event {
  STARK_SIGHTED("Stark sighted"), WARSHIPS_APPROACHING("Warships approaching"), TRAITOR_DETECTED(
      "Traitor detected");

-  private String description;
+  private final String description;

  Event(String description) {
    this.description = description;
--- a/event-aggregator/src/main/java/com/iluwatar/event/aggregator/EventEmitter.java
+++ b/event-aggregator/src/main/java/com/iluwatar/event/aggregator/EventEmitter.java
@ -31,7 +31,7 @@ import java.util.List;
 */
 public abstract class EventEmitter {

-  private List<EventObserver> observers;
+  private final List<EventObserver> observers;

  public EventEmitter() {
    observers = new LinkedList<>();
--- a/event-aggregator/src/main/java/com/iluwatar/event/aggregator/Weekday.java
+++ b/event-aggregator/src/main/java/com/iluwatar/event/aggregator/Weekday.java
@ -36,7 +36,7 @@ public enum Weekday {
  SATURDAY("Saturday"),
  SUNDAY("Sunday");

-  private String description;
+  private final String description;

  Weekday(String description) {
    this.description = description;
--- a/event-aggregator/src/main/java/com/iluwatar/event/aggregator/module-info.java
+++ b/event-aggregator/src/main/java/com/iluwatar/event/aggregator/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.eventaggregator {
-	requires org.slf4j;
-}
--- a/event-aggregator/src/test/java/com/iluwatar/event/aggregator/KingJoffreyTest.java
+++ b/event-aggregator/src/test/java/com/iluwatar/event/aggregator/KingJoffreyTest.java
@ -74,7 +74,7 @@ public class KingJoffreyTest {
  }

  private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();

    public InMemoryAppender(Class<?> clazz) {
      ((Logger) LoggerFactory.getLogger(clazz)).addAppender(this);
--- a/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/Event.java
+++ b/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/Event.java
@ -33,9 +33,9 @@ public class Event implements IEvent, Runnable {

  private static final Logger LOGGER = LoggerFactory.getLogger(Event.class);

-  private int eventId;
-  private int eventTime;
-  private boolean isSynchronous;
+  private final int eventId;
+  private final int eventTime;
+  private final boolean isSynchronous;
  private Thread thread;
  private boolean isComplete = false;
  private ThreadCompleteListener eventListener;
--- a/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/EventManager.java
+++ b/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/EventManager.java
@ -43,8 +43,8 @@ public class EventManager implements ThreadCompleteListener {
  public static final int MAX_ID = MAX_RUNNING_EVENTS;
  public static final int MAX_EVENT_TIME = 1800; // in seconds / 30 minutes.
  private int currentlyRunningSyncEvent = -1;
-  private Random rand;
-  private Map<Integer, Event> eventPool;
+  private final Random rand;
+  private final Map<Integer, Event> eventPool;

  private static final String DOES_NOT_EXIST = " does not exist.";

--- a/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/module-info.java
+++ b/event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/module-info.java
@ -1,26 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-module com.iluwatar.eventasynchronous {
-	requires org.slf4j;
-}
--- a/event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserCreatedEvent.java
+++ b/event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserCreatedEvent.java
@ -32,7 +32,7 @@ import com.iluwatar.eda.model.User;
 */
 public class UserCreatedEvent extends AbstractEvent {

-  private User user;
+  private final User user;

  public UserCreatedEvent(User user) {
    this.user = user;
--- a/Show More
+++ b/Show More