Introduction

Swapping two numbers is a basic programming task that can be accomplished in several ways. This guide will show you how to swap two numbers in Java using different methods, including using a temporary variable, arithmetic operations, and bitwise XOR.

Problem Statement

Given two numbers, swap their values so that the first number takes the value of the second, and the second takes the value of the first.

Example:

Input: a = 5, b = 10
Output: a = 10, b = 5

Solution Steps

Approach 1: Using a Temporary Variable

Store the First Number: Use a temporary variable to store the value of the first number.
Swap the Values: Assign the value of the second number to the first number, and then assign the value stored in the temporary variable to the second number.

Approach 2: Using Arithmetic Operations

Add the Numbers: Add both numbers and store the result in the first variable.
Subtract the Second Number: Subtract the second number from the first variable and store the result in the second variable.
Subtract the New Second Number: Subtract the new second number from the first variable and store the result in the first variable.

Approach 3: Using Bitwise XOR

XOR the Numbers: XOR both numbers and store the result in the first variable.
XOR the First Variable with the Second: XOR the first variable with the second and store the result in the second variable.
XOR the First Variable with the Second Again: XOR the first variable with the second and store the result in the first variable.

Approach 1: Using a Temporary Variable

/**
 * Java Program to Swap Two Numbers using a Temporary Variable
 * Author: https://www.javaguides.net/
 */
public class SwapUsingTempVariable {

    public static void main(String[] args) {
        int a = 5;
        int b = 10;

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

        // Using a temporary variable to swap
        int temp = a;
        a = b;
        b = temp;

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

Output for Approach 1

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Explanation for Approach 1

Store the First Number: The value of a is stored in the temporary variable temp.
Swap the Values: The value of b is assigned to a, and the value in temp (original value of a) is assigned to b.

Approach 2: Using Arithmetic Operations

/**
 * Java Program to Swap Two Numbers using Arithmetic Operations
 * Author: https://www.javaguides.net/
 */
public class SwapUsingArithmetic {

    public static void main(String[] args) {
        int a = 5;
        int b = 10;

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

        // Swapping using arithmetic operations
        a = a + b;  // a now becomes 15
        b = a - b;  // b now becomes 5 (15 - 10)
        a = a - b;  // a now becomes 10 (15 - 5)

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

Output for Approach 2

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Explanation for Approach 2

Add the Numbers: The sum of a and b is stored in a.
Subtract the Second Number: The value of b is subtracted from a (which now contains the sum), and the result is stored in b.
Subtract the New Second Number: The value of b (which now holds the original value of a) is subtracted from a (which still contains the sum), and the result is stored in a.

Approach 3: Using Bitwise XOR

/**
 * Java Program to Swap Two Numbers using Bitwise XOR
 * Author: https://www.javaguides.net/
 */
public class SwapUsingXOR {

    public static void main(String[] args) {
        int a = 5;
        int b = 10;

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

        // Swapping using bitwise XOR
        a = a ^ b;  // a now becomes 15 (binary: 1111)
        b = a ^ b;  // b now becomes 5 (binary: 0101)
        a = a ^ b;  // a now becomes 10 (binary: 1010)

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

Output for Approach 3

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Explanation for Approach 3

XOR the Numbers: The XOR of a and b is stored in a.
XOR the First Variable with the Second: The XOR of the new a (which now contains the XOR of the original a and b) and b is stored in b, giving b the original value of a.
XOR the First Variable with the Second Again: The XOR of the new a (which now contains the XOR of the original a and b) and the new b (which now contains the original value of a) is stored in a, giving a the original value of b.

Conclusion

These three approaches demonstrate different ways to swap two numbers in Java. The first approach using a temporary variable is the most straightforward and easiest to understand. The second approach, using arithmetic operations, avoids using extra space but may lead to overflow with large numbers. The third approach using bitwise XOR is a clever technique that also avoids extra space but may be less intuitive for beginners. Each method is effective, and the choice of which to use depends on the specific requirements and constraints of your program.