Advantages of Abstraction and Polymorphism in Java

 

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  • What is the difference between an interface and abstract class? 32 answers

    • Simply saying: interface is a contract, abstract class is skeletal implementation. (Additionally, in Java interfaces are mostly used because it's not possible to extend multiple classes.)

    Contract says what, implementation says how.

    Example of interface: java.util.List . It has all methods that any list should have: add() , size() , indexOf() and so on.

    Example of abstract class: java.util.AbstractList . Though it has many abstract methods, some List methods, that don't depend on the way elements are stored in the concrete list, are implemented there ( addAll() , equals() , toString() and others). To create complete implementation, not all List methods should be implemented, thus making implementor's work easier.

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