How to swap two number without third variable

This  is  simple  but  some  time  make you  brain teaser  at interview .  Just  simple  and try
 yourself

public class SwapNumber {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num1 = 20;

int num2 = 90;

System.out.println("Before Swapping");

System.out.println("Value of num1 is :" + num1);

System.out.println("Value of num2 is :" +num2);

//add both the numbers and assign it to first

num1 = num1 + num2;

num2 = num1 - num2;

num1 = num1 - num2;

System.out.println("Before Swapping");

System.out.println("Value of num1 is :" + num1);

System.out.println("Value of num2 is :" +num2);

    }

}

    

This  is  out put  of code.

Before Swapping

Value of num1 is :20

Value of num2 is :90

Before Swapping

Value of num1 is :90

Value of num2 is :20