#554: Subclass Sandbox pattern (#998)

* Fix issue #761: ThreadSafeDoubleCheckLocking.java: Instantiating by Reflection call will be successful if you do that firstly

* Create leader election module

* Create Interface of Instance and MessageManager

* Create implementations with token ring algorithm

* Change package structure.
Create basic message system.

* Implement heartbeat and heartbeat invoking message system

* Implement election message handler

* Add leader message handler

* Add main entry point

* Add comments

* Update README.md

* Fix checkstyle issue

* Add Unit Tests

* Add Unit Tests

* Add bully leader selection

* Change System.out to log print.
Add MIT license in each file.

* Add More java doc comments

* Add unit test

* Add unit tests

* Add subclass-sandbox

* Add Unit Test

* Add Unit Test

* Fix Typo

* Move dependency into parent pom.xml

* Change local valuable reference to be var

pom.xml

@@ -60,6 +60,7 @@
         <jaxb-api.version>2.3.1</jaxb-api.version>
         <jaxb-impl.version>2.3.2</jaxb-impl.version>
         <annotation-api.version>1.3.2</annotation-api.version>
+        <system-rules.version>1.19.0</system-rules.version>
     </properties>
     <modules>
         <module>abstract-factory</module>
@@ -180,8 +181,8 @@
         <module>bytecode</module>
         <module>leader-election</module>
         <module>data-locality</module>
+        <module>subclass-sandbox</module>
         <module>circuit-breaker</module>
-
     </modules>
 
     <repositories>
@@ -317,6 +318,12 @@
                 <artifactId>javassist</artifactId>
                 <version>3.25.0-GA</version>
             </dependency>
+            <dependency>
+                <groupId>com.github.stefanbirkner</groupId>
+                <artifactId>system-rules</artifactId>
+                <version>${system-rules.version}</version>
+                <scope>test</scope>
+            </dependency>
         </dependencies>
     </dependencyManagement>