Java Program to Reverse a Number

In this blog post, we will learn how to write a Java program to reverse a number step by step.

Reversing a number might seem like a trivial task, but when you’re just starting with programming, it can be a fun and challenging problem.

The Problem Statement 

Given a number, say 12345, we want to reverse it, so the result will be 54321.

Program Explanation 

Before writing the program, let’s break down the process into steps: 

Initialize the reversed number: Start with a variable called reversed and set it to 0. 

Loop until the number is not zero: The loop will serve to extract digits from the original number one by one. 

Extract the last digit: Use the modulo operator % to get the last digit of the number. 

Append the extracted digit to the reversed number: Multiply the reversed number by 10 (to shift its digits to the left) and then add the extracted digit. 

Remove the last digit from the original number: Use the division operator / to remove the last digit. 

Repeat: Continue the process until the original number is 0. 

Java Program 

As per above program explanation, let's write the Java program to reverse a number:

public class ReverseNumber {

    public static int reverse(int number) {
        int reversed = 0; // Step 1:Initialize the reversed number
        while (number != 0) { // Step 2: Loop until the number is not zero
            int digit = number % 10;          // Step 3: Extract the last digit
            reversed = reversed * 10 + digit; // Step 4: Append the digit to reversed
            number = number / 10;             // Step 5: Remove the last digit
        }
        return reversed;
    }

    public static void main(String[] args) {
        int originalNumber = 12345;
        int reversedNumber = reverse(originalNumber);
        System.out.println("Original Number: " + originalNumber);
        System.out.println("Reversed Number: " + reversedNumber); 
    }
}

Output:

Original Number: 12345
Reversed Number: 54321

Understanding Core Logic

int digit = number % 10: This line of code finds the remainder when our number is divided by 10, which effectively gives us the last digit of the number. 

reversed = reversed * 10 + digit: Here, we shift the digits of reversed to the left by multiplying by 10, then add the extracted digit. This effectively appends the digit to the end. 

number = number / 10: By dividing the number by 10, we remove its last digit.

Conclusion 

In this post, we learned how to write a Java program to reverse a number step by step and we understood the core logic of the program.

Happy coding!