INTERFACES

An interface in java is a blueprint of a class. It has static constants and abstract methods only.

The interface in java is a mechanism to achieve fully abstraction. There can be only abstract methods in the java interface not method body. It is used to achieve fully abstraction and multiple inheritance in Java.

Java Interface also represents IS-A relationship.

It cannot be instantiated just like abstract class.

Why use Java interface?

There are mainly three reasons to use interface. They are given below.

• It is used to achieve fully abstraction.
• By interface, we can support the functionality of multiple inheritance.
• It can be used to achieve loose coupling.

The java compiler adds public and abstract keywords before the interface method and public, static and final keywords before data members.

In other words, Interface fields are public, static and final bydefault, and methods are public and abstract.

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Understanding relationship between classes and interfaces

As shown in the figure given below, a class extends another class, an interface extends another interface but a class implements an interface.

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Simple example of Java interface

In this example, Printable interface have only one method, its implementation is provided in the A class.

1. interface printable{  
2. void print();  
3. }  
4.   
5. class A6 implements printable{  
6. public void print(){System.out.println("Hello");}  
7.   
8. public static void main(String args[]){  
9. A6 obj = new A6();  
10. obj.print();  
11.  }  
12. }  

Output:Hello