Java program to reverse an integer number

Reverse an integer java – Java Program to Reverse an Integer Number

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Reverse an integer java: In the previous article, we have seen Java Program to Test if a double Number is an Integer

In this article we are going to see how to reverse a number using java programming language.

Java Program to Reverse an Integer Number

How to reverse an int in java: While reversing a number last numbers will come to first. See below examples to understand it clearly.

Example:
Number: 12343 Then Reverse: 34321
Number 891 Then Reverse: 189

Let’s see different ways to reverse a number.

Method-1: Java Program to Reverse an Integer Number By Using Static Input Value

Approach:

  1. Declare an int variable say ‘num‘ and assign value to it, which needs to be reversed.
  2. Declare a variable rev = 0 to store the reversed number.
  3. Run a while loop until the given number becomes zero.
  4. Inside the while loop, extract the last digit using %(modulo) operator (num % 10) and add it to 10 times the value of rev.
  5. Remove the last digit from the number by dividing it with 10.
  6. Print the number outside the loop

Program:

public class Main
{
    public static void main(String[] args) 
    {
        //an integer number declared
        int num = 12345;
        //intger variable 'rev' to store reverse value
        int rev = 0;
        
        //find reverse using while loop
        while (num != 0) 
        {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }
        System.out.println("Reversed num: " + rev);
    }
}

Output:

Reversed num: 54321

Method-2: Java Program to Reverse an Integer Number By Using User Input Value

Approach:

  1. Declare an int variable say ‘num‘ and take value of it as user input, which needs to be reversed.
  2. Declare a variable rev = 0 to store the reversed number.
  3. Run a while loop until the given number becomes zero.
  4. Inside the while loop, extract the last digit using %(modulo) operator (num % 10) and add it to 10 times the value of rev.
  5. Remove the last digit from the number by dividing it with 10.
  6. Print the number outside the loop

Program:

import java.util.*;

public class Main
{
    public static void main(String[] args) 
    {
        //Scanner class object craeted
        Scanner sc=new Scanner(System.in);
        //taking user input of a Number
         System.out.print("Enter a number: ");
        int num = sc.nextInt();
        //intger variable 'rev' to store reverse value
        int rev = 0;
        
        //find reverse using while loop
        while (num != 0) 
        {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }
        System.out.println("Reversed number: " + rev);
    }
}

Output:

Enter a number: 4567
Reversed number: 7654

Method-3: Java Program to Reverse an Integer Number By Using User Defined Method

Approach:

  1. Declare an int variable say ‘num‘ and take value of it as user input, which needs to be reversed.
  2. Then call a user defined method reverse() and pass that num as argument.
  3. Inside method declare a variable rev = 0 to store the reversed number and run a while loop until the given number becomes zero.
  4. Inside the while loop, extract the last digit using %(modulo) operator (num % 10) and add it to 10 times the value of rev.
  5. Remove the last digit from the number by dividing it with 10.
  6. Print the number outside the loop

Program:

import java.util.*;

public class Main
{
    public static void main(String[] args) 
    {
        //Scanner class object craeted
        Scanner sc=new Scanner(System.in);
        //taking user input of a Number
         System.out.print("Enter a number: ");
        int num = sc.nextInt();
        //callling reverse() method
        reverse(num);
    }
    
    //user defined method reverse() to find reverse
    public static void reverse(int num)
    {
        //intger variable 'rev' to store reverse value
        int rev = 0;
        
        //find reverse using while loop
        while (num != 0) 
        {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }
        System.out.println("Reversed number: " + rev);
    }
}

Output:

Enter a number: 876
Reversed number: 678

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