public static void main(String[] args) {
    int[] arr = {4, 7, 5, 6, 2};
    System.out.println(determineGreatestNum(arr, 0, arr[0]));
    }

static public int determineGreatestNum(int[] arr, int index, int currentGreatest){

        if (index == arr.length)
            return currentGreatest;

        if (arr[index] > currentGreatest)
            currentGreatest = arr[index];

        index += 1;
        return determineGreatestNum(arr, index, currentGreatest);
    }
}