What is Upcasting and Downcasting in Java

 

What is Up Casting and Down Casting in Java,in this article i will step through a sample program and explain when you need to use Up casting and when you need to use Down casting .

In this Sample Program i have created 3 Class

1. robot  class -> Which is the super Class
2. terminator_X_1 -> Which is the Child Class inherit the robot Class
3. acessBot Class -> Which Access the robot and terminator_X_1 class

What is Up casting ?

Up Casting  is used , when we want to access Function or information in the Super Class. In this Case the Super Class is robot

What is Down Casting ?

Down  Casting  is used , when we want to access specific behavior in the child Class.

 

Robot Class

 

package updowncast;

public class robot {
	
	public void start(){
		
		System.out.println("Robot Start");
	}
	
    public void recalibrate(){
		
		System.out.println("Robot recalibrate");
	}
    public void move (){
		
		System.out.println("Robot Moving");
	}
	

}

 

Terminator_X_1 Class

 

package updowncast;

public class terminator_X_1 extends robot {
	
   public void start(){
		
		System.out.println("Robot Start");
	}
    
   public void shooting(){
	   
	    System.out.println("Terminator is Shooting");
	   
   }

}

 

accessBot Class

 

package updowncast;

public class acessBot {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		//robot robot_1 = new robot();
		terminator_X_1 Arnold = new terminator_X_1();
		
		
		//Up casting
		
		robot robot_1 = Arnold;
		robot_1.recalibrate();
		
		// Down Casting
		
		robot robot_2 = new terminator_X_1();
		terminator_X_1 genesis = (terminator_X_1)robot_2;
		genesis.shooting();
		
		
	
	}

}

 

Program Explanation 

1. First , I have created a super class called Robot .
2. In the Robot Class i have created 3 Method start() recalibrate () move()
3. Then i created the child class terminator_X_1 which inherit the robot super class
4. In the terminator_X_1 class i have created 2 Method start() and shoot()
5. Then I have created a class called accessBot to access the robot and terminator_X_1 class
6. Up casting
7. I created a new terminator_X_1 called Arnold
8. I cast Arnold into the new robot Object robot_2
9. Then I access the robot class recalibrate() to re calibrate Arnold
10. Why is that so ?
11. You donot want Arnold to access / and know how to recalibrate himself right!!
12. Down Casting
13. Then i created an object called robot_2
14. robot_2 is a new terminator_X_1
15. terminator_X_1 genesis = (terminator_X_1)robot_2; this statement is asking ? So now robot_2 is a terminator_X_1 type and your new terminator_X_1 object is named genesis
16. /lastly i access the terminator_X_1 method ” genesis.shooting()

Chcek out Numerical Casting in Java here