SwapNumbers.java

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/*Java Program to swap two numbers from user input*/
import java.util.Scanner;

public class SwapNumbers {

    public static void main(String[] args) {

        int a, b; // declare 2 int type variables a, b. a and b will hold the input from user

        Scanner scanner = new Scanner(System.in); // Create an object of Scanner class

        System.out.println("Enter First Number");
        a = scanner.nextInt(); // initialize a variable with first number entered by user.

        System.out.println("Enter Second Number");
        b = scanner.nextInt(); // initialize b variable with second number entered by user.


        System.out.println("--Before swap--");
        System.out.println("First number = " + a);
        System.out.println("Second number = " + b);

        /* create another variable and name it temporary. 
		'a' variable will give its value to
		'temporary' variable because 'a' will hold the value of 'b'
		variable. and we don't want previous value of 'a' to be 
		lost or replaced by new value of 'b' variable that's why we created a 'temporary'. Once 'b'
		will give its value to 'a' variable then 'b' will get value from temporary variable*/
        int temporary = a; // here we are plassing the value to 'a' to 'temporary'. now a is ready to hold another value of 'b'

        a = b; // Here 'a' is replacing by value of 'b' and 'b' is ready to take value of 'a' from 'temporary' variable

        // Value of temporary (which contains the initial value of a) is assigned to b
        b = temporary;

        System.out.println("--After swap--");
        System.out.println("First number = " + a);
        System.out.println("Second number = " + b);
    }
}

/*----------OUTPUT----------
Enter First Number
5
Enter Second Number
10
--Before swap--
First number = 5
Second number = 10
--After swap--
First number = 10
Second number = 5
*/