Chapter 6. Interfaces and Inner Classes

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• Interfaces

• Object Cloning

• Interfaces and Callbacks

• Inner Classes

• Proxies

You have now seen all the basic tools for object-oriented programming in Java. This chapter shows you several advanced techniques that are commonly used. Despite their less obvious nature, you will need to master them to complete your Java tool chest.

The first, called an interface, is a way of describing what classes should do, without specifying how they should do it. A class can implement one or more interfaces. You can then use objects of these implementing classes anytime that conformance to the interface is required. After we cover interfaces, we take up cloning an object (or deep copying, as it is sometimes called). A clone of an object is a new object that has the same state as the original. In particular, you can modify the clone without affecting the original.

Next, we move on to the mechanism of inner classes. Inner classes are technically somewhat complex they are defined inside other classes, and their methods can access the fields of the surrounding class. Inner classes are useful when you design collections of cooperating classes. In particular, inner classes enable you to write concise, professional-looking code to handle GUI events.

This chapter concludes with a discussion of proxies, objects that implement arbitrary interfaces. A proxy is a very specialized construct that is useful for building system-level tools. You can safely skip that section on first reading.

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