Java Program to Find Sum of All Numbers in an Array by Using Recursion

Java Program to Find Sum of All Numbers in an Array by Using Recursion

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Prerequisite: Recursion in Java

In the previous article, we have discussed about Java Program to Print Fibonacci Series by Using Recursion

In this program we are going to see how to find sum of all numbers in an Array by using Recursion in Java programming language.

Java Program to Find Sum of All Numbers in an Array by Using Recursion

Lets assume there is an array say A which has 5 elements {1,2,3,4,5}

So, sum of the elements of array A = 1+2+3+4+5 = 15

Now let’s see different ways to find sum of all numbers in an Array by using Recursion.

Method-1: Java Program to Find Sum of All Numbers in an Array by Using Static Input and Recursion

Approach:

  • Declare and initiate an integer variable Array say ‘A’.
  • Call a user defined method calculateSum() and pass the array ‘A’ and the size of the array i.e. ‘A.length’ as parameter.
  • Inside the user defined method we will check the size of the Array. If the size of the array is <= 0 then the method returns 0 else it calls the same method as calculateSum(A, n-1) + A[n-1] and return the value to the main method.
  • Now the value of the user defined method calculateSum() is stored in an integer variable say ‘sum’.
  • Print the value of sum.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        //declare and initialize an array A
        int A[] = {1,2,3,4,5};
        //call the user defined method calculateSum()
        //and store the result value inside an integer variable say ‘sum’
        int sum = calculateSum(A, A.length);
        //print the result
        System.out.println("The sum of the Array is: "+sum);
    }
    
    //calculateSum() method 
    static int calculateSum(int A[], int n)
    {   
        //checking if array has no element then returning 0 as result
        if (n<= 0)
            return 0;
        //else array has some elements
        //and adding all the array elements by calling the calculateSum() method recursively
        else
            //using recursion technique
            return calculateSum(A,n-1) + A[n-1];
    }
}

Output:

The sum of the Array is: 15

Method-2: Java Program to Find Sum of All Numbers in an Array by Using Dynamic Input and Recursion

Approach:

  • Declare an integer variable say ‘n‘ which holds the array size, take it’s value input from user.
  • Declare an integer variable Array say ‘A’ with array size as  ‘n‘
  • Take input of array elements from user by using a for loop.
  • Call a user defined method calculateSum() and pass the array ‘A’ and the size of the array i.e. ‘A.length’ as parameter.
  • Inside the user defined method we will check the size of the Array. If the size of the array is <= 0 then the method returns 0 else it calls the same method as calculateSum(A, n-1) + A[n-1] and return the value to the main method.
  • Now the value of the user defined method calculateSum() is stored in an integer variable say ‘sum’.
  • Print the value of sum.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        // create a scanner class object
        Scanner s = new Scanner(System.in);
        System.out.println("Enter number of elements you want in array:");
        //take the array size input from user
        int n = s.nextInt();
        // declare the array 
        int A[] = new int[n];
        System.out.println("Enter all the elements:");
        //Take input of all the elements sequentially from user
        for(int i = 0; i < n; i++)
        {
            A[i] = s.nextInt();
        }
        //call the user defined method calculateSum()
        //and store the result value inside an integer variable say ‘sum’
        int sum = calculateSum(A, A.length);
        //print the result
        System.out.println("Sum of the Array elements: "+sum);
    }
    
    //calculateSum() method 
    static int calculateSum(int A[], int n)
    {   
        //checking if array has no element then returning 0 as rsult
        if (n<= 0)
            return 0;
        //else array has some elements
        //and adding all the array elements by calling the calculateSum() method recursively
        else
            //using recursion technique
            return calculateSum(A,n-1) + A[n-1];
    }
}

Output:

Enter number of elements you want in array:
4
Enter all the elements:
10 20 30 40
Sum of the Array elements: 100

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