extend : Java Glossary

2006-02-23 by Roedy Green ©1996-2008 Canadian Mind Products
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extend

When you derive a class from a base class we say the derived subclass extends the base class. An interface can also extend another interface. In contrast, when a class provides the methods (possibly abstract) necessary to conform to some interface we say that class implements the interface. Extending a class is closely related to implementing an interface. A new class can extend at most one superclass, but it may implement several interfaces.

In interface may extend several other interfaces. You sometimes do this to give you a short same to stand for the requirement implementing half a dozen related interfaces.

Extending means adding new method definitions. Implementing means satisfying the existing interface contract by writing the proscribed method bodies. Logically, when you extend an abstract class and fill in the method bodies, that should be called implementing, but in the Java world that is called extending.

implement
inheritance
multiple inheritance

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