Summary: In this programming example, we will learn to reverse a number in Java.

Example:

```Input:  123
Output: 321

Input:  5821
Output: 1285```

There are multiple ways to reverse a number in Java. Let’s discuss each method one by one.

## Method 1: Using While Loop

1. Input a number (`num`).
2. Loop while `num!=0`:
1. Extract the last digit from `num` using `num%10` and concatenate it to the reverse (`rev`).
2. Remove the last digit from `num` using `num/10`.
3. Output the reverse.
``````import java.util.Scanner;

public class Main{
public static void main(String args[]){
Scanner in = new Scanner(System.in);
int num, rev =0, digit;

//Input a number
System.out.print("Enter a number: ");
num = in.nextInt();

//loop until num!=0
while(num!=0){
digit = num%10;          //extract last digit
rev = 10*rev + num%10;   //append the digit to the reverse
num = num/10;            //remove the last digit
}

//output the reverse
System.out.println("Reversed Number: "+rev);
}
}``````

Output:

Enter a number: 123
Reversed Number: 321

## Method 2: Without Using Another Variable

Unlike the above method, instead of appending the digits to the reverse vairiable, we can output them directly.

``````import java.util.Scanner;

public class Main {
public static void main(String args[]){
Scanner in = new Scanner(System.in);

//Input a number
System.out.print("Enter a number: ");
int num = in.nextInt();

System.out.print("Reversed Number: ");

//loop until num!=0
while(num!=0){
System.out.print(num%10);    //extract last digit and output
num = num/10;                //remove the last digit from num
}
}
}``````

Output:

Enter a number: 1009
Reversed Number: 9001

The concept of reversing a number in java is useful in checking palindrome numbers.

### This Post Has One Comment

1. Smruti Sandhya Singh

Plzzz give all the questions answer and programs of icse 10