Interface in Java

 Interface in Java

What is Interfaces

• Another way to achieve abstraction in Java, is with interfaces. It’s a blueprint of a class, which tells by class what to do not how to do.

• An interface is a completely "abstract class" that is used to group related methods with empty bodies. 

Features of Interfaces

• It is used to achieve abstraction.

• It supports multiple inheritance.

• It can be used to achieve loose coupling

• Like abstract classes, interfaces cannot be used to create objects

• Interface methods do not have a body - the body is provided by the "implement" class

• On implementation of an interface, you must override all of its methods

• Interface methods are by default abstract and public

• Interface attributes are by default public, static and final

• An interface cannot contain a constructor (as it cannot be used to create objects)

Why and When to use Interfaces

1) To achieve security - hide certain details and only show the important details of an object (interface).

2) Java does not support "multiple inheritance" (a class can only inherit from one superclass). However, it can be achieved with interfaces, because the class can implement multiple interfaces. Note: To implement multiple interfaces, separate them with a comma.

         Ex. Class A implements B, C, D{

}

Java Interface Example

In this example, the Printable interface has only one method, and its implementation is provided in the A6 class.

1. interface printable{  
2. void print();  
3. }  
4. class A6 implements printable{  
5. public void print(){System.out.println("Hello");}  
6.   
7. public static void main(String args[]){  
8. A6 obj = new A6();  
9. obj.print();  
10.  }  
11. }

Output:

Hello

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