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Reverse An Integer In Java

Reverse An Integer In Java

Reverse an Integer in Java is a part of our Java code examples series. This is a very common question for junior level java developers.

Interview Problem Statement

  • Reverse an integer in Java without using any API.
  • Reverse a number in Java.

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Code Example

package com.adevguide.java.problems;

public class ReverseInteger {

    public static void main(String[] args) {
        // Variable to hold input value
        Integer input = 123;
        // Variable to hold reversed value
        Integer reverse = 0;
        // loop till input value becomes zero
        while (input != 0) {
            // multiple previous reverse value by 10 , add the remainder to it and save it back
            // in reverse variable
            reverse = reverse * 10 + input % 10;
            // Divide input by 10 and store quotient value in input
            input = input / 10;
        }
        // Print reverse Value
        System.out.println("Reverse Integer ::" + reverse);
    }

}

 

Code Explanation

To reverse an integer in Java, we will follow the following steps:

  1. Find one’s place of the input and add it to 10 x previously calculated reverse value.
  2. Change input value to the quotient of division of input by 10.

Example:

Input = 123

Iteration 1:

reverse = 0 * 10 + 123 % 10

reverse = 3

Input = 12

Iteration 2:

reverse = 3 * 10 + 12 % 10

reverse = 32

Input = 1

Iteration 3:

reverse = 32 * 10 + 1 % 10

reverse = 321

Input = 0

Source Code

As always, you can find all our source code at GitHub.

GitHub Link