Java Program:

Example:

import java.util.Scanner;
public class Armstrong {
  public static void main(String []args) {
    int num,num2,digit,sum=0;
    Scanner userInput = new Scanner(System.in);
    System.out.print("Enter your number : ");
    num = userInput.nextInt();
    num2=num;
    while(num!=0) {
      digit=num%10;
      sum= sum + digit*digit*digit;
      num/=10;
    }

    if(num2==sum)System.out.println("Armstrong Number");
    else System.out.println("Not a Armstrong Number");
  }
}

Output:

  Enter Your number : 407
  Armstrong Number

You must know first,

Armstrong Number : if a number & cube of every single digit of the number are equal than the number is an Armstrong number

Example :

Number: 407 & cube of every single digit = 407. so it's an Armstrong Number
(4*4*4)+(0*0*0)+(7*7*7) = 64+0+343 = 407

//Save the original number
  num2=num;

//find every single digit & add the cube of it
  while(num!=0) {
  digit=num%10;
  sum=sum + digit*digit*digit;
  num/=10;
}

//check for the Armstrong
if(num2==sum)