Why an Interface is used in a Java Program

Since we have Classes in Java program
Then what is the need for An Interface in a Java Program
Please explain to me
i'm confused

These are fair comments as per as interface is concern.... we need interface to declare the methods without implementing the methods. Basically interfaces help implementing classes in a organised way.
Now We got abstract class also, which has got more or less same features like interfaces. In abstract class also we can declare a method without implementation.
If we use abstract class and extend that abstract class, we don't have implement all the abstract methods in that particular class,which would extend the abstract class, but if we implement an interface in a class, we have to define all the methods with their body. Now, can anyone tell me , in a generic way, when do we use interface and when do we use abstract class. I don't need the differences between abstract class and interface...that i know...thanks in advance
take it easy
RD
l

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this problem:
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full years he has been in office, you get the number
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Why an Interface is used in a Java Program

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