How to reverse number in Java?

Reversing Numbers in Java: A Comprehensive Guide

Introduction

Reversing numbers is a fundamental operation in programming that involves swapping the digits of a number from the most significant digit to the least significant digit. In this article, we will explore the different ways to reverse numbers in Java, including manual reversal and using built-in methods.

Manual Reversal

Manual reversal involves iterating through the digits of a number and swapping them with the next digit. Here’s an example of how to do it:

public class ManualReversal {

    public static void main(String[] args) {

        int num = 12345;

        System.out.println("Original Number: " + num);

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

        int reversedNum = reverseNumber(num);

        System.out.println("Reversed Number: " + reversedNum);

    }



    public static int reverseNumber(int num) {

        int reversedNum = 0;

        while (num != 0) {

            int digit = num % 10;

            reversedNum = reversedNum * 10 + digit;

            num /= 10;

        }

        return reversedNum;

    }

}

Using Built-in Methods

Java provides several built-in methods to reverse numbers. Here are a few examples:

Method	Description
Integer.parseInt(String str)	Converts a string to an integer.
Integer.toString(int num)	Converts an integer to a string.
String.valueOf(int num)	Converts an integer to a string.
Math.abs(int num)	Returns the absolute value of an integer.
Math.pow(int num, int exp)	Returns the power of an integer.

Here’s an example of how to use these methods to reverse a number:

public class BuiltInReversal {

    public static void main(String[] args) {

        int num = 12345;

        System.out.println("Original Number: " + num);

        System.out.println("Reversed Number: " + Integer.toString(reverseNumber(num)));

    }



    public static int reverseNumber(int num) {

        return Integer.parseInt(String.valueOf(Math.abs(num)));

    }

}

Using a Loop

Here’s an example of how to reverse a number using a loop:

public class LoopReversal {

    public static void main(String[] args) {

        int num = 12345;

        System.out.println("Original Number: " + num);

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

        int reversedNum = reverseNumber(num);

        System.out.println("Reversed Number: " + reversedNum);

    }



    public static int reverseNumber(int num) {

        int reversedNum = 0;

        while (num != 0) {

            int digit = num % 10;

            reversedNum = reversedNum * 10 + digit;

            num /= 10;

        }

        return reversedNum;

    }

}

Using a StringBuilder

Here’s an example of how to reverse a number using a StringBuilder:

public class StringBuilderReversal {

    public static void main(String[] args) {

        int num = 12345;

        System.out.println("Original Number: " + num);

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

        StringBuilder sb = new StringBuilder();

        sb.append(num);

        int reversedNum = Integer.parseInt(sb.reverse().toString());

        System.out.println("Reversed Number: " + reversedNum);

    }

}

Table: Reversing Numbers in Java

Method	Description
Manual Reversal	Iterates through the digits of a number and swaps them with the next digit.
Built-in Methods	Converts a string to an integer, converts an integer to a string, and returns the absolute value of an integer.
Loop	Uses a loop to iterate through the digits of a number and swap them with the next digit.
StringBuilder	Uses a StringBuilder to reverse a string.

Conclusion

Reversing numbers is a fundamental operation in programming that can be achieved using various methods. In this article, we explored the different ways to reverse numbers in Java, including manual reversal, using built-in methods, and using a loop. We also discussed the use of a StringBuilder to reverse a string. By understanding how to reverse numbers in Java, you can write more efficient and effective code.