Java program to swap two numbers with and without a third variable

In this post we explain two methods to swap two numbers in Java.

Method 1: swapping two numbers using a third variable

Method 2: swapping two numbers without a third variable.

1. Java program to swap two numbers using a third variable.

This is the simplest method to swap two numbers. We can swap two variables using a third or temporary (temp) variable by following the steps below:

Step 1: The value of the variable A is stored in the temp variable

temp = A;

Step 2: Once the value of A is stored, we can store the value of B in A

A = B;

Step 3: And finally the initial value of A (temp) is stored in B:

B = temp;

For example,

A = 1

B = 2

	A	B	temp
	1	2	-
temp = A	1	2	1
A = B	2	2	1
B = temp	2	1	1

It can also be done by first storing the value of B.

temp = B;

B = A;

A = temp;

Here is the complete Java code to swap two numbers using a temp variable:

import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int A, B, temp;
        System.out.print("Input the first number: ");
        A = input.nextInt();
        System.out.print("Input the second number: ");
        B = input.nextInt();
        System.out.println("Before swapping: A = " + A + "   B = " + B);                                          
      
        temp = A;
        A = B;
        B = temp;
       
        System.out.println("After swapping: A = " + A + "   B = " + B);
    }
}

Sample output:

Input the first number: 1     
Input the second number: 2
Before swapping: A = 1   B = 2
After swapping: A = 2   B = 1

2. Java program to swap two numbers without third variable.

We can swap two numbers without a temp variable just by using arithmetic operators.

A and B are the variables to swap. The arithmetic operations to swap them are one addition followed by two subtractions.

A = A + B;

B = A – B;

A = A – B;

For example,

A = 2

B = 3

 

	A	B
	2	3
A = A + B	5	3
B = A - B	5	2
A = A - B	3	2

 

We can also swap them by performing one multiplication followed by two divisions:

A = A * B;

B = A / B;

A = A / B;

 

	A	B
	2	3
A = A * B	6	3
B = A / B	6	2
A = A / B	3	2

Here is the complete Java code to swap two numbres without third variable using the addition-subtraction method:

import java.util.Scanner;
 
public class JavaApplication360 {
 
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int A, B;
        System.out.print("Input the first number: ");
        A = input.nextInt();
        System.out.print("Input the second number: ");
        B = input.nextInt();
        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);
    }
}

Sample output:

Input the first number: 2     
Input the second number: 3
Before swapping: A = 2   B = 3
After swapping: A = 3   B = 2