Composition and Inheritance

[Mathews P Srampikal]

What is the difference between Composition and Inheritance in java.
Thanks.

[Ernest Friedman-Hill]

In Java, or in any language, inheritance is, well, inheritance -- as expressed by the "extends" keyword; while composition refers to the inclusion of one object inside another as a member.
In this example, Bar gets access to Foo's capabilites via inheritance:

class Foo { }
class Bar extends Foo { }

While here it gets them via composition:

class Foo { }
class Bar { Foo f = new Foo(); }

The general, oversimplified rule is to use composition when you can, inheritance when you must.