Merge branch 'master' of https://github.com/iluwatar/java-design-patterns

* 'master' of https://github.com/iluwatar/java-design-patterns: (27 commits)
  Remove use of coveralls-maven-plugin (sonarqube.com covers this)
  Add SonarQube.com badge
  Fix environment variable
  Add Travis instructions for SonarQube.com analysis
  Adds more criticism to Singleton pattern.
  Event Based Asynchronous pattern: Add missing license header and puml diagram
  Changed config to non-interactive
  Moved config into a separate dir
  Unused import removed.
  End process logic clause has been corrected.
  Caching pattern: Documentation and diagram
  Fixes #437. Adds criticism to Singleton pattern.
  Alter JUnit tests to run in lesser time.
  Updated version snapshot to 1.14.0
  Changes based on review feedback.
  Closes #436. Adds criticism to service locator pattern.
  Caching pattern: Implementation of Cache-Aside pattern
  Caching pattern: Style fix for null check
  Caching pattern: Refactor LRU cache to avoid NPE and unnecessary cache lookup
  Caching pattern: Refactor shutdown hook to use method reference
  ...

singleton/README.md

@@ -36,6 +36,13 @@ Use the Singleton pattern when
 * [java.lang.System#getSecurityManager()](http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#getSecurityManager--)
 
 
+## Consequences
+
+* Violates Single Responsibility Principle (SRP) by controlling their own creation and lifecycle.
+* Encourages using a global shared instance which prevents an object and resources used by this object from being deallocated.     
+* Creates tightly coupled code that is difficult to test.
+* Makes it almost impossible to subclass a Singleton.
+
 ## Credits
 
 * [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)