Here is the list of Gang of Four patterns related with an actual implementation in Java EE. Read on – it will make sense (hopefully).
Strategy: EJB interface.
Defines a family of algorithms, encapsulates each one and makes them interchangeable. Strategy lets the algorithm vary independently from clients who use it.
Decorator: Dependency Injection.
Attach additional responsibilities to an object dynamically. Provide a flexible alternative to sub-classing for extending functionality.
Factory: EJBs .
Define an interface for creating an object, but let the subclasses decide which class to instantiate.
Decoupled requester and handler. Chain the handlers, one of them must handle it.
Ensure a class only has one instance, and provide a global point of access
Flyweight: JDBC Connection Pooling.
Adapter : Use the same interface, but adapt to other classes.
Façade: Single point of entry for a sub-system.
Template: Defer implementation to subclass.
Builder: For complex varying structures.
Iterator: Access items in any collection implementation.