Java Program to Swap Two Numbers Without Using a Third Variable

In this Java program, we will learn how to swap two numbers without using a third or temporary variable.

For example, if:

a = 10
b = 20

After swapping:

a = 20
b = 10

Java Program

We can swap two numbers using arithmetic operators without requiring a third variable.

import java.util.Scanner;

public class SwapWithoutThirdVariable {

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

        System.out.print("Enter second number: ");
        int b = sc.nextInt();

        System.out.println("Before Swapping:");
        System.out.println("a = " + a);
        System.out.println("b = " + b);

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

        System.out.println("After Swapping:");
        System.out.println("a = " + a);
        System.out.println("b = " + b);
        sc.close();
    }
}

Output

Enter first number: 10
Enter second number: 20

Before Swapping:
a = 10
b = 20

After Swapping:
a = 20
b = 10

Explanation

The swapping is performed using three arithmetic operations:

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

Suppose:

a = 10
b = 20

The first statement adds both values:

a = 10 + 20 = 30

Now:

a = 30
b = 20

The second statement calculates the original value of a:

b = 30 - 20 = 10

Now:

a = 30
b = 10

Finally, the third statement calculates the original value of b:

a = 30 - 10 = 20

Therefore:

a = 20
b = 10

The two values have been successfully swapped without using a third variable.

Alternative Method Using XOR

For integer values, two numbers can also be swapped without a third variable using the XOR (^) operator:

a = a ^ b;
b = a ^ b;
a = a ^ b;

However, the addition/subtraction approach is generally easier for beginners to understand.

Important Note

The addition/subtraction method can cause integer overflow if a + b exceeds the range of the int data type. For production code, using a temporary variable is usually clearer and safer.

Key Points

• No third or temporary variable is used.
• The values are swapped using arithmetic operations.
• The program works with Java 8 and later versions.
• XOR can also be used as an alternative for integer values.

Conclusion

Swapping two numbers without a third variable is a common Java programming interview question. The addition and subtraction method provides a simple way to exchange two integer values without using an additional variable.