Question

Write a recursive method to sum the values in an array of integers. Create a file ArraySum.java and add the recursive method public int sumOfArray (). Use the driver class ArraySumDriver.java to populate your array and demonstrate that your method works.

////ArraySumDriver.java///////
public class ArraySumDriver {
   private final static int ARRAY_SIZE = 6;

   /**
    * @param args
    */
   public static void main(String[] args) {
      int index = 0;

      Integer[] myArray = new Integer[ARRAY_SIZE];
      ArraySum arraySum = new ArraySum();
      
      myArray[index++] = 3;
      myArray[index++] = 5;
      myArray[index++] = 2;
      myArray[index++] = 6;
      
      int sum = arraySum.sumOfArray(myArray, 3);
      System.out.println(sum);
      
      myArray[index++] = 7;
      myArray[index++] = 1;
      
      sum = arraySum.sumOfArray(myArray, 5);
      System.out.println(sum);
   }

}

Answer 1

JAVA PROGRAM

class ArraySum // create class ArraySum
{
//implement sumOfArray() method with two arugments
//First argument Integer array a and Second argument int size
public int sumOfArray(Integer a[],int size)
{
if(size<=0) return 0; // check condition size<=0 then return 0
return sumOfArray(a,size-1)+a[size-1]; // else, call recusively sumOfArray() and calculate sum of array elements
}
}

// Implement Driver class ArraySumDriver
public class ArraySumDriver
{
// declre final static integer ARRAY_SIZE=6
// does not change ARRAY_SIZE it is final
private final static int ARRAY_SIZE=6;

public static void main(String [] args)
{
   int index=0; // declare constant integer index=0
   Integer [] myArray=new Integer[ARRAY_SIZE]; // create Integer array object
   ArraySum arraySum=new ArraySum(); // create instance of ArraySum is arraySum
   // declare array elements one by one
   myArray[index++]=3;
   myArray[index++]=5;
   myArray[index++]=2;
   myArray[index++]=6;
  
   int sum=arraySum.sumOfArray(myArray,3); // calling sumOfArray() method and return result sum
   System.out.println(sum); // display sum of only first 3 elements in array

   myArray[index++]=7;
   myArray[index++]=1;

   sum=arraySum.sumOfArray(myArray,5); // calling sumOfArray() method and return result sum
   System.out.println(sum); // display sum of only first 5 elements in array
}
}

OUTPUT

10
23