Find Sum of Digits of a Number Using Recursion in Java

In this article, we will understand how to find the sum of the digits of a number using recursion in Java. A recursive function is a function that calls itself multiple times until a particular condition or base condition is met.

In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

Problem Statement

Write a program in Java to find the sum of the digits of a number using recursion. Below is a demonstration of the same.

Input Enter the number : 12131415
Output The Sum of digits of 12131415 is 18

Sum of Digits of a Number

Below are the different approaches to find the sum of the digits of a number using recursion -

• Using user-defined input
• Using predefined input

User-Defined Input

Following are the steps to find the sum of the digits of a number using user-defined input -

• First, we will import the Scanner class from the java.util package.

• After that, we will initialize a Scanner object to read input from the user.

• Display a message asking the user to enter a number.

• Take the user input using the nextInt() method of the Scanner object.
  

• Invoke the digitSum function, passing the user input as an argument.
  

• Print the output, showing the sum of the digits of the entered number.
  

Example

Here, the input is being entered by the user based on a prompt.

import java.util.Scanner;
public class Sum{
   public static void main(String args[]){
      int my_input, my_result;
      Scanner my_scanner = new Scanner(System.in);
      System.out.print("Enter the number : ");
      my_input = my_scanner.nextInt();
      my_result = digitSum(my_input);
      System.out.println("The Sum of digits of " + my_input + " is " + my_result);
   }
   static int digitSum(int n){
      if (n == 0)
         return 0;
      return (n % 10 + digitSum(n / 10));
   }
}

Output

Enter the number : 12131415
The Sum of digits of 12131415 is 18

Using Predefined Input

Following are the steps to find the sum of the digits of a number using predefined input -

• Declare and initialize an integer variable with a predefined value (e.g., 12131415).

• Print the predefined number to the console.

• Invoke the digitSum function, passing the predefined number as an argument.
  

• Print the result, showing the sum of the digits of the predefined number.
  

Example

Here, the integer has been previously defined, and its value is accessed and displayed on the console -

public class Sum{
   public static void main(String args[]){
      int my_input = 12131415;
      System.out.println("The number is defined as : " +my_input);
      int my_result = digitSum(my_input);
      System.out.println("The Sum of digits of " + my_input + " is " + my_result);
   }
   static int digitSum(int n){
      if (n == 0)
         return 0;
      return (n % 10 + digitSum(n / 10));
   }
}

Output

The number is defined as : 12131415
The Sum of digits of 12131415 is 18