System Design

1. singleton pattern

Singleton design pattern in java

http://howtodoinjava.com/2012/10/22/singleton-design-pattern-in-java/

**a thorough explanation of singleton pattern**

2. factory pattern

Factory design pattern in java

http://howtodoinjava.com/2012/10/23/implementing-factory-design-pattern-in-java/

3. abstract factory pattern

Abstract factory pattern in java

http://howtodoinjava.com/2012/10/29/abstract-factory-pattern-in-java/

4. prototype pattern

Prototype design pattern in java

http://howtodoinjava.com/2013/01/04/prototype-design-pattern-in-java/