Thread: Divide and conquer Algorithm

I am learning divide and conquer algorithms in school and I am having some trouble figuring it out. I am required to find the sum of an array but divide and conquering an array to base case 4 then finding the sum of those 4 numbers. I think I have the basic idea of divide and conquer, but I cannot get my code below to work.

I keep getting this error
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8
at getSum.sumArray(getSum.java:17)
at getSum.sumArray(getSum.java:21)
at getSum.main(getSum.java:7)

public class getSum {
	static int sum = 0;
	public static void main(String[] args) {
			int[] numbers = {2,2,2,2,2,2,2,2};
			int amount = 0;
	       amount = sumArray(0,numbers.length,numbers);
	       System.out.print(amount);
	}
 
	public static int sumArray(int first, int last, int[] A){
		int index = last - first;
		if(index == 1){
			return sum;
		}else if(index <= 4 && index > 1){
			for(int i = first; first < last; i++){
				sum += A[i];
			}
			return sum;
		}
		return (sumArray(first, last / 2, A) + sumArray(last / 2, A.length, A));
	}
}