Design patterns usage in java

Design patterns are used and supported extensively throughout the Java APIs. Here are some examples:

The Model-View-Controller design pattern is used extensively throughout the Swing API.

The getInstance() method in java.util.Calendar is an example of a simple form of the Factory Method design pattern.

The classes java.lang.System and java.sql.DriverManager are examples of the Singleton pattern, although they are not implemented using the approach recommended in the GoF book but with static methods.

The Prototype pattern is supported in Java through the clone() method defined in class Object and the use of java.lang.Cloneable interface to grant permission for cloning.

The Java Swing classes support the Command pattern by providing an Action interface and an AbstractAction class.

The Java 1.1 event model is based on the observer pattern. In addition, the interface java.util.Observable and the class java.util.Observer provide support for this pattern.

The Adapter pattern is used extensively by the adapter classes in java.awt.event.

The Proxy pattern is used extensively in the implementation of Java's Remote Method Invocation (RMI) and Interface Definition Language (IDL) features.

The structure of Component and Container classes in java.awt provide a good example of the Composite pattern.

The Bridge pattern can be found in the separation of the components in java.awt (e.g., Button and List), and their counterparts in java.awt.peer.