Interfaces in Java

An interface is like a class, which has methods and variable, but declared methods are by default abstract(means no method signature, no body). An Interface is also called blueprint of the class.

Points To Remember :

• To declare an interface, we use "interface" keyword.
•  It is used to provide total abstraction. 
• All the methods in an interface are declared with an empty body are public and abstract by default 
• All fields are public, static and final by default.

Syntax :

interface interface_name {
    
    // declare fields
    // declare methods
}

Why do we use interface?

• It is used to achieve total abstraction.

• Since Java does not support multiple inheritance in case of class, but it can be achieved by the use of an interface.

• It is also used to achieve loose coupling.

Program to understand the concept of an interface :

interface A {

       int a=10; //by default public, static, final

      void display(); // by default public and abstract   

 }

class Demo implements A {

        public void display()

        {

           System.out.println("Hello world");

        }

       public static void main(String args[])

        {

            Demo obj = new Demo();

             obj.display();

             System.out.println(a);

         }

 }

OUTPUT:

Hello world

10