Java - What is Abstraction in Java

http://javarevisited.blogspot.de/2010/10/abstraction-in-java.html

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Abstraction in Java is achieved by using interface and abstract class

What is abstract class in Java

Java has concept of abstract classes, abstract method but a variable can not be abstract in Java.

An abstract method in Java doesn't have body , its just a declaration. In order to use abstract method you need to override that method in sub class.

Abstraction Using Interface in Java

In Java Interface is an another way of providing abstraction, Interfaces are by default abstract and only contains public, static, final constant or abstract methods.

Abstraction : Things to Remember

1) In Java you can not create instance of abstract class using new operator, its compiler error. Though abstract class can have constructor.

2) Abstract class can contain both abstract and concrete method. Abstract method doesn't have body, just declaration.

3) A class automatically becomes abstract class when any of its method declared as abstract.

4) In Java, variable can not be made abstract , its only class or methods which would be abstract.