Examples of GoF Design Patterns in Java's core libraries

Answer 1

RMI is based on Proxy.

Should be possible to cite one for most of the 23 patterns in GoF:

1. Abstract Factory: java.sql interfaces all get their concrete implementations from JDBC JAR when driver is registered.
2. Builder: java.lang.StringBuilder.
3. Factory Method: XML factories, among others.
4. Prototype: Maybe clone(), but I'm not sure I'm buying that.
5. Singleton: java.lang.System
6. Adapter: Adapter classes in java.awt.event, e.g., WindowAdapter.
7. Bridge: Collection classes in java.util. List implemented by ArrayList.
8. Composite: java.awt. java.awt.Component + java.awt.Container
9. Decorator: All over the java.io package.
10. Facade: ExternalContext behaves as a facade for performing cookie, session scope and similar operations.
11. Flyweight: Integer, Character, etc.
12. Proxy: java.rmi package
13. Chain of Responsibility: Servlet filters
14. Command: Swing menu items
15. Interpreter: No directly in JDK, but JavaCC certainly uses this.
16. Iterator: java.util.Iterator interface; can't be clearer than that.
17. Mediator: JMS?
18. Memento:
19. Observer: java.util.Observer/Observable (badly done, though)
20. State:
21. Strategy:
22. Template:
23. Visitor:

I can't think of examples in Java for 10 out of the 23, but I'll see if I can do better tomorrow. That's what edit is for.