Armstrong Number in Java

Last updated: February 8, 2025

An Armstrong Number (also known as a Narcissistic Number) is a number that is equal to the sum of its own digits each raised to the power of the number of digits. In this blog, we will understand the concept and learn how to check Armstrong numbers using Java.

What is an Armstrong Number?

A number with n digits is an Armstrong number if:

sum = digit₁ⁿ + digit₂ⁿ + digit₃ⁿ + ... + digitₙⁿ
  

If the sum equals the original number, it is an Armstrong number.

Examples

• 153 → 1³ + 5³ + 3³ = 153
• 370 → 3³ + 7³ + 0³ = 370
• 9474 → 9⁴ + 4⁴ + 7⁴ + 4⁴ = 9474

Java Program to Check Armstrong Number

Below is a simple Java program using loops and math logic:

import java.util.Scanner;

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

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

        int original = num;
        int sum = 0;

        // count digits
        int digits = String.valueOf(num).length();

        while (num > 0) {
            int digit = num % 10;
            sum += Math.pow(digit, digits);
            num /= 10;
        }

        if (sum == original) {
            System.out.println(original + " is an Armstrong Number.");
        } else {
            System.out.println(original + " is NOT an Armstrong Number.");
        }
    }
}
  

Optimized Version

A slightly optimized solution that avoids converting the number to string:

public static boolean isArmstrong(int num) {
    int digits = 0, temp = num;

    // count digits
    while (temp > 0) {
        temp /= 10;
        digits++;
    }

    int sum = 0;
    temp = num;

    while (temp > 0) {
        int digit = temp % 10;
        sum += Math.pow(digit, digits);
        temp /= 10;
    }

    return sum == num;
}
  

Conclusion

Armstrong numbers are a classic programming exercise useful for practicing loops, conditionals, and mathematical logic in Java. Try modifying the program to find Armstrong numbers in a range or generate all Armstrong numbers up to 10000.