Armstrong Number or Not Java Program

Checking whether a number is an Armstrong number in Java program is a classic fresher‑level interview question that tests both logical thinking and coding skills. An Armstrong number is a number that is equal to the sum of its digits each raised to the power of the total number of digits.

For Example-

371 is an Armstrong number because it has 3 digits, and
371 = 3³ + 7³ + 1³ = 27 + 343 + 1 = 371
9474 is also an Armstrong number since it has 4 digits, and
9474 = 9⁴ + 4⁴ + 7⁴ + 4⁴ = 6561 + 256 + 2401 + 256 = 9474
By definition, 0 and 1 are considered Armstrong numbers too.

Check given number Armstrong number or not

So let's write a Java program to check whether a given number is an Armstrong number or not. We'll break down how the logic works step by step later.

import java.util.Scanner;

public class ArmstrongNumber {
  public static void main(String[] args) {
    System.out.println("Please enter a number : ");
    Scanner scanIn = new Scanner(System.in);
    int scanInput = scanIn.nextInt();
    boolean isArmstrong = checkForArmstrongNo(scanInput);
    if(isArmstrong){
     System.out.println(scanInput + "  is an Armstrong number");
    }else{
     System.out.println(scanInput + " is not an Armstrong number"); 
    }
    scanIn.close();
  }
 
  private static boolean checkForArmstrongNo(int number){
    // convert number to String
    String temp = number + "";
    int numLength = temp.length();
    int numCopy = number;
    int sum = 0;
    while(numCopy != 0 ){
      int remainder = numCopy % 10;
      // using Math.pow to get digit raised to the power
      // total number of digits
      sum = sum + (int)Math.pow(remainder, numLength);
      numCopy = numCopy/10;
    }
    System.out.println("sum is " + sum );
    return (sum == number) ? true : false;
  }
}

Some outputs-

Please enter a number : 
125
sum is 134
125 is not an Armstrong number

Please enter a number : 
371
sum is 371
371  is an Armstrong number

Please enter a number : 
54748
sum is 54748
54748  is an Armstrong number

Armstrong number Java program explanation

In an Armstrong number Java program, the input number is first taken from the user. To determine the number of digits, the simplest approach is to convert the number into a string and use its length. This gives us the power to which each digit must be raised.

The logic works as follows:

Extract digits one by one
- Start from the last digit using the modulus operator (num % 10).
- Raise this digit to the power of the total number of digits.
Accumulate the sum
- Add the powered value to a running total.
- Reduce the number by one digit using integer division (num / 10).
Repeat until all digits are processed
- Continue the loop until the number becomes zero.
Compare with the original number
- If the accumulated sum equals the original number, it is an Armstrong number.
- Otherwise, it is not.

That's all for this topic Armstrong Number or Not Java Program. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Monday, April 13, 2026