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A positive number is called an Armstrong number if it is equal to the cubic sum of that number. For example, 0, 1, 153, 370, 371, 407.

For example:

Lets take 153

153 = (111)+(555)+(333)

(111)=1
(555)=125
(333)=27
So:
1+125+27=153

Program to check number is Armstrong Number or not

public class ArmstrongNumber {

  public static void main(String[] args) {

    int num = 407;
    int rem = 0;
    int tempNumber = 0;
    int sum = 0;

    tempNumber = num;
    while (tempNumber != 0) {
      rem = tempNumber % 10;
      sum = sum + rem * rem * rem;
      tempNumber = tempNumber / 10;
    }

    if (sum == num) {
      System.out.println(num + " is an Armstrong number");
    } else {
      System.out.println(num + " is not an Armstrong number");
    }
  }
}

Output

407 is an Armstrong number

Program to check number is Armstrong Number or not using for loop

public class ArmstrongNumber {

  public static void main(String[] args) {

    int num = 153;
    int rem = 0;
    int tempNumber = 0;
    int sum = 0;

    tempNumber = num;

    for (; tempNumber != 0; tempNumber /= 10) {
      rem = tempNumber % 10;
      sum = sum + rem * rem * rem;
    }

    if (sum == num) {
      System.out.println(num + " is an Armstrong number");
    } else {
      System.out.println(num + " is not an Armstrong number");
    }
  }
}

Output

153 is an Armstrong number

Program to Check Armstrong number for n digits

An Armstrong number is an n-digit base b number such that the sum of its (base b) digits raised to the power n is the number itself.
Example:
1634= 1^4 + 6^4 + 3^4 + 4^4 = 1+1296+81+256 = 1634

public class ArmstrongNumber {

  public static void main(String[] args) {

    int number = 1634;
    int tempNumber = 0;
    int rem = 0;
    int value = 0;
    int n = 0;

    tempNumber = number;

    for (; tempNumber != 0; tempNumber /= 10, n++);

      tempNumber = number;
    
    for (; tempNumber != 0; tempNumber /= 10) {
      rem = tempNumber % 10;
      value += Math.pow(rem, n);
    }
    

    if (value == number) {
      System.out.println(number + " is an Armstrong number.");
    } else {
      System.out.println(number + " is not an Armstrong number.");

    }
  }
}

Output

1634 is an Armstrong number.