Online Ethical Hacking Course

Apply Now

Examples

How to Find Sum of Digits of a Number in Java?

Let’s learn the multiple ways to find the sum of digits of a number in Java! 

The sum of digits is a common mathematical operation that involves adding up all the individual digits in a given number. Understanding different techniques to find the sum of digits in Java is essential for various applications, ranging from verifying the validity of identification numbers to solving complex maths problems.

Here, you will know and understand the different ways to calculate the sum of digits of a number in Java. Each method offers its own unique advantages, enabling you to choose the most suitable approach for specific scenarios and optimize your code for efficiency.

So, let’s get started and practice the Java program for sum of digits of a number!

Sum of Digits in Java Using while loop

The following program calculates the sum of digits of number in Java using loop:

Code

import java.util.Scanner;

public class SumOfDigitsCalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");

        int number = scanner.nextInt();
        if (number < 0) {
            System.out.println("Please enter a non-negative integer.");
        } else {
            int sumOfDigits = calculateSumOfDigits(number);
            System.out.println("Sum of digits of " + number + " is: " + sumOfDigits);
        }
    }

    private static int calculateSumOfDigits(int n) {
        int sum = 0;
        while (n != 0) {
            int digit = n % 10; // Extract the last digit of the number
            sum += digit; // Add the digit to the sum
            n /= 10; // Remove the last digit from the number
        }
        return sum;
    }
}

Output

Enter a number: 678
Sum of digits of 678 is: 21

Explanation

In this program, we use the Scanner class to take input from the user. The user is prompted to enter a number, and the program calculates the sum of its digits using a while loop.

The calculateSumOfDigits method takes an integer n as input and initializes a variable sum to store the sum of digits. In the while loop, we extract the last digit of the number using the modulo operator %, add it to the sum, and then remove the last digit from the number by dividing it by 10.

This process continues until all the digits have been processed, and the sum of all digits is calculated and returned. 

Full Stack Developer Course

Sum of Digits in Java Using Recursion

Here's a Java program that calculates the sum of digits of a given number using recursion:

Code

import java.util.Scanner;

public class SumOfDigitsCalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a non-negative integer: ");

        int number = scanner.nextInt();
        if (number < 0) {
            System.out.println("Please enter a non-negative integer.");
        } else {
            int sumOfDigits = calculateSumOfDigits(number);
            System.out.println("Sum of digits of " + number + " is: " + sumOfDigits);
        }
    }

    private static int calculateSumOfDigits(int n) {
        if (n < 10) {
            return n; // Base case: If n is a single-digit number, return itself
        } else {
            return n % 10 + calculateSumOfDigits(n / 10); // Recursive case: Add last digit and call recursively for remaining digits
        }
    }
}

Output

Enter a number: 4728
Sum of digits of 4728 is: 21

Explanation

In this program, we use recursion to calculate the sum of digits of a given number. The calculateSumOfDigits method takes an integer n as input.

The base case is when n is a single-digit number (i.e., less than 10). In the base case, the method returns n itself, as the sum of a single-digit number is the number itself.

The recursive case is when n is greater than or equal to 10. In the recursive case, we calculate the sum of the last digit of n (obtained using % 10) and the sum of digits of the remaining part of n (obtained using / 10) by making a recursive call to the calculateSumOfDigits method.

This process continues until n becomes a single-digit number, and the sum of all digits is calculated and returned. 

Learn Next: