Java Program to Swap Two Numbers Without a Temporary Variable

Two numbers can be swapped without a third variable by storing information about both values in one of them. This page shows three tricks: addition and subtraction, the XOR operator, and multiplication and division. They are popular interview questions, but each has limits, which are explained below.

1. Swap Using Addition and Subtraction

With a = 10 and b = 20:

• a = a + b; makes a 30 (the sum of both).
• b = a - b; makes b 30 - 20 = 10 (the old a).
• a = a - b; makes a 30 - 10 = 20 (the old b).

public class SwapWithoutTemp {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        System.out.println("Before swapping: a = " + a + ", b = " + b);

        a = a + b;
        b = a - b;
        a = a - b;

        System.out.println("After swapping:  a = " + a + ", b = " + b);
    }
}

Before swapping: a = 10, b = 20
After swapping:  a = 20, b = 10

2. Swap Using the XOR Operator

The bitwise XOR operator ^ has the property that x ^ y ^ y == x. Applying it three times swaps the values without any risk of overflow. This version reads the numbers from the user.

import java.util.Scanner;

public class SwapXor {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter first number: ");
        int a = scanner.nextInt();
        System.out.print("Enter second number: ");
        int b = scanner.nextInt();
        scanner.close();

        a = a ^ b;
        b = a ^ b;   // (a ^ b) ^ b = a
        a = a ^ b;   // (a ^ b) ^ a = b

        System.out.println("After swapping: first = " + a + ", second = " + b);
    }
}

Enter first number: 2000
Enter second number: 4000
After swapping: first = 4000, second = 2000

3. Swap Using Multiplication and Division

The same idea works with * and /, but it fails if either number is 0 (division by zero) and can overflow for large values. It is shown here only for completeness.

public class SwapMultiply {
    public static void main(String[] args) {
        int a = 6;
        int b = 9;
        System.out.println("Before swapping: a = " + a + ", b = " + b);

        a = a * b;   // 54
        b = a / b;   // 6
        a = a / b;   // 9

        System.out.println("After swapping:  a = " + a + ", b = " + b);
    }
}

Before swapping: a = 6, b = 9
After swapping:  a = 9, b = 6

4. Summary

• a = a + b; b = a - b; a = a - b; swaps two numbers without a third variable.
• The XOR version a ^= b; b ^= a; a ^= b; works for integers and never overflows.
• The multiply and divide version fails when a value is 0.
• In real code, a temporary variable is clearer and works for every type.

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