A basic program that gets input number (Integer) from the user and prints whether the number is Armstrong Number or not.

By this program, you can understand the usage of commandline arguments, use of arithmetic operators, printing variables, Armstrong Number Logic and more.

In an Armstrong Number, the sum of cube of individual digits is equal to number itself. In other words the following equation will hold true

  xy..z = x^3 + y^3+.....+ z^3

where n is number of digits in number

For example this is a 3 digit Armstrong number

  370 = (3)^3 + (7)^3 + (0)^3
  = 27 + 343 + 0
  = 370

Examples of Armstrong Numbers

  0, 1, 153, 370, 371, 407, etc.

Task: Print whether the given number is Armstrong Number or not ...

  Eg: number = 153
  Final Output: 
      [->] 153 is a Armstrong Number.
          
  Eg: number = 2
  Final Output:
      [->] 2 is not a Amrstrong Number.
         

The filename must have the same name as the public class name, This is to ensure that the Java Virtual Machine (JVM) understands the entry point of the program

To run the program, open your commandline and type the following:

• Without Commandline Arguments

 $ ..\JavaBasic> javac .\ArmstrongNumber\ArmstrongNumber.java
 $ ..\JavaBasic> java ArmstrongNumber.ArmstrongNumber

• Defined Arguments

 -> argument-1: 
      name: number
      type: integer
      help: Used to specify the input number.

• With Commandline Arguments

 $ ..\JavaBasic> javac .\ArmstrongNumber\ArmstrongNumber.java
 $ ..\JavaBasic> java ArmstrongNumber.ArmstrongNumber 370

package ArmstrongNumber;

import java.util.Scanner; // used to get user input

public class ArmstrongNumber {
    private static boolean isArmstrongResult = false;
    private static int number = -1;
    public static void main(String[] args) {
        if (args.length > 0) {
            if (args.length == 1) {
                number = Integer.parseInt(args[0]);
                isArmstrongResult = isArmstrong(number);
            }
            else
                System.out.println("[!] Available arguments: [number]");

        } else {
            Scanner scan = new Scanner(System.in);
            System.out.print("[<-] Enter the number to check: ");
            number = scan.nextInt();
            scan.close(); // closing the scanner input stream as it is no longer required.
            isArmstrongResult = isArmstrong(number);
        }

        if (isArmstrongResult)
            System.out.println("[->] " + number + " is a Armstrong Number.");
        else
            System.out.println("[->] " + number + " is not a Armstrong Number.");
    }

    public static boolean isArmstrong(int number) {
        // this method will return true if the given number is an Armstrong number.
        int armstrongSum = 0, rem;
        int checkNumber = number; // storing the original number value to check whether the armstrong sum = number
        while (number > 0){
            rem = number % 10; // gets the last digit of input number. EX: gets 3 from 123
            number /= 10; // removing the last digit of input number. Ex: 123 becomes 12
            armstrongSum += (int) Math.pow(rem, 3);
        }
        return armstrongSum == checkNumber;
    }
}

import java.util.Scanner; : imports Scanner class from java > util package. Scanner is a class that lets you get input form the user. Scanner can take any primitive data type as input from the user.

public static void main(String[] args) : main method/function is the first method that will be executed in any java programs.

String[] args : args is a array of String type. It is used to get commandline arguments for your program.

args.length > 0 : checks whether args is empty or not

System.out.println(); : Prints the String and changes output cursor to next line

Scanner scan = new Scanner ( System.in ); : scan is an object(a special variable that stores the address in RAM/main memory) of the class Scanner. Here scan acts as the variable that has the access to System.in stream (An input stream that connects keyboard input to the program.

scan.nextInt() : gets Integer input from user.

scan.close(); : closes the input stream link/pipe.

Math.pow(base, exponent) : A predefined method to find the power of a number.