nested for loop question

[javabob]

say i have the following nested for loops

Code:

for(x1 = 1; x1 < b; x1++)
    for(x2 = 1; x2 < b; x2++)
         for(x3 = 1; x3 < b; x3++)
             y+=x1 * x2 * x3

I want the user to input integers a and b, where there are 'a' nested for loops
(goes up to xa) and then output an integer y, In the above example a = 3 , since I won't know what a and b are beforehand I can't hand write the for loops. I tried using recursion but still can't solve the problem after working for several hours and I dont even know if that's the best way to go. Can somebody at least show me a correct first step to solving this problem?

[bksamrat]

it shud surly work wit recursion!! if I wer in ur place I ud do it wit recursin function!! put som mor time.. that's the best way!!

[hardwired]

Code:

import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        System.out.printf("%3s %3s %3s %5s %3s%n",
                          "x1", "x2", "x3", "next", "y");
        int a = 3;
        int b = 4;
        int x1, x2, x3, y = 0;
        for(x1 = 1; x1 < b; x1++) {
            for(x2 = 1; x2 < b; x2++) {
                for(x3 = 1; x3 < b; x3++) {
                    int next = x1 * x2 * x3;
                    y += next;
                    System.out.printf("%2d  %2d  %2d  %3d  %4d%n",
                                       x1, x2, x3, next, y);
                }
            }
        }
        System.out.printf("desired y = %d%n", y);

        y = 0;
        int[] counts = new int[a];
        Arrays.fill(counts, 1);
        int index = counts.length-1;
        int lastCount = counts.length-1;
        boolean more = true;
        do {
            int product = 1;
            for(int i = 0; i < counts.length; i++) {
                product *= counts[i];
            }
            y += product;
            System.out.printf("index = %d counts = %s  product = %2d  y = %3d%n",
                               index, Arrays.toString(counts), product, y);
            more = !isDone(counts, b-1);
            if(counts[lastCount] == b-1) {
                index = shiftUp(counts, index, b-1);
            } else {
                counts[lastCount]++;
            }
        } while(more);
        System.out.printf("loop y = %d%n", y);
    }

    private static int shiftUp(int[] counters, int index, int max) {
        int nextIndex = counters.length-1;
        while(counters[nextIndex] == max && nextIndex > 0) {
            counters[nextIndex] = 1;
            nextIndex--;
        }
        for(int i = nextIndex+1; i < counters.length; i++) {
            counters[i] = 1;
        }
        counters[nextIndex]++;
        return nextIndex;
    }

    private static boolean isDone(int[] counters, int limit) {
        for(int i = 0; i < counters.length; i++) {
            if(counters[i] < limit)
                return false;
        }
        return true;
    }
}

[javabob]

Thank you very much for taking the time to help me. I had a similar approach but i couldn't get the finer details in even after hours of thinking. If you did all that in less than an hour, then you sir are a genious(at least from my point of view)