Java Program for calculating Armstrong number. 153 is an armstrong number as 1^(number of digits)+5^(number of digits)+3^(number of digits)=153. Similarly 371 is an armstrong number 3^(number of digits)+7^(number of digits)+1^(number of digits)=371.

Armstrong.java

import java.util.Scanner;
import java.util.InputMismatchException;

public class Armstrong{
    
    public static void main(String args[]){
      
      Scanner sc=new Scanner(System.in);    
        
      System.out.print("Enter a number : ");
      long input=-999,number=-999,copyOfInput=-999;
        try{
        input=sc.nextLong();   
        number=input;  
        copyOfInput=input;    
        }catch(InputMismatchException ime){
          System.err.println("Error : Please enter a valid number ");
          System.exit(1);    
        }
         
        // To count the number of digits in the number, it will be needed for armstrong calculation
        int numberOfDigits=0;
        while(number >0){
          numberOfDigits++;
          number=number/10;
        }        
       
        // Actual Armstrong Calculation
        long sum=0;int remainder=0;
        while(input >0){
            remainder=(int)input%10;
            sum=sum+(long)Math.pow(remainder,numberOfDigits);
            input=input/10;
        }
        
        if(copyOfInput == sum){
         System.out.println("Number "+copyOfInput+" is an Armstrong Number");   
        }else{
         System.out.println("Number "+copyOfInput+" is not an Armstrong Number");   
        }
        
    }
    
    
    
    
    
}