Q 11) Interfaces

Interfaces : 

•  Interfaces are pure abstract classes (100 %) and are similar to classes.
• An interface cannot be instantiated, meaning you cannot create an instance of an interface.
• It can be implemented by a class or extended by another interface.
• Interfaces are used to achieve complete abstraction in java.

Syntax :

interface interface_name {

            }

Example of interface :

public interface DriveCar {

          void turnLeft();

          void turnRight();

void moveBack();

void accelerate();

}

The above is equivalent to :

public interface DriveCar {

                   public abstract void turnLeft();

                   public abstract void turnRight();

          public abstract void moveBack();

          public abstract void accelerate();

}

Rules for using Interface:-

• Methods inside interface must be static, final, native or strict fp.
• All variable declared in interface are implicitly public, static and final (Constants).
• All methods are public and abstract by default, Even if you don’t use the keywords (Therefore 100 % abstract).
• Interface cannot implement a class.
• Interface can extend one or more interfaces.
• Java doesn’t support multiple inheritance, but a class can implement more than one interface.
•  Interface must implement all the methods in its class.

Example program 1 :

package org.javanoobs.interfaces;

public interface Movable {

    

     void move();

}

package org.javanoobs.interfaces;

public class Vehicle implements Movable{

    

     public void move(){

          

           int avgSpeed = 40;

           System.out.println(" Average speed is :  " +avgSpeed);

     }

    

     public static void main(String[] args) {

          

           Vehicle vh = new Vehicle();

           vh.move();

     }

}

Output :

Average speed is :  40

Example program 2:

package org.javanoobs.interfaceinheritance;

// This is the first interface.

public interface Movable {

    

     boolean isMovable();

}

package org.javanoobs.interfaceinheritance;

// this is the second interface.

public interface Rollable {

    

     boolean isRollable();

}

package org.javanoobs.interfaceinheritance;

public class Tyre implements Movable,Rollable {

    

     int width;

    

     public boolean isMovable(){

          

           System.out.println(" This is inside of isMovable method... ");

          

           return true;

     }

    

     public boolean isRollable(){

          

           System.out.println(" This is inside of isRoallable method ");

           return true;

     }

    

     public static void main(String[] args) {

          

           Tyre tr = new Tyre();

           System.out.println(tr.isMovable());

           System.out.println(tr.isRollable());

          

          

     }

}

Output :

This is inside of isMovable method...

true

 This is inside of isRoallable method

true