all index.md files renamed to README.md for more compatibility with github

singleton/README.md

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+---
+layout: pattern
+title: Singleton
+folder: singleton
+permalink: /patterns/singleton/
+categories: Creational
+tags:
+ - Java
+ - Gang Of Four
+ - Difficulty-Beginner
+---
+
+## Intent
+Ensure a class only has one instance, and provide a global point of
+access to it.
+
+![alt text](./etc/singleton_1.png "Singleton")
+
+## Applicability
+Use the Singleton pattern when
+
+* there must be exactly one instance of a class, and it must be accessible to clients from a well-known access point
+* when the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code
+
+## Typical Use Case
+
+* the logging class
+* managing a connection to a database
+* file manager
+
+## Real world examples
+
+* [java.lang.Runtime#getRuntime()](http://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#getRuntime%28%29)
+
+## Credits
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)
+* [Effective Java (2nd Edition)](http://www.amazon.com/Effective-Java-Edition-Joshua-Bloch/dp/0321356683)