Question

I want to write a Java function that will get as input either int[], float[] or double[]. The algorithm is exactly the same (some kind of a scalar product). How can I write a single function that will be able to handle all types of numeric arrays?

Answer 1

You can write one method to do them all, however, it won’t be anywhere near as readable of efficient. You have to make a choice between what is a generic or an efficient solution.

public static void main(String... args) throws IOException {
    int[] nums = new int[10*1000 * 1000];
    {
        long start = System.nanoTime();
        product2(nums);
        long time = System.nanoTime() - start;
        System.out.printf("Took %.3f seconds to take the product of %,d ints using an int[].%n", time / 1e9, nums.length);
    }
    {
        long start = System.nanoTime();
        product(nums);
        long time = System.nanoTime() - start;
        System.out.printf("Took %.3f seconds to take the product of %,d ints using reflections.%n", time / 1e9, nums.length);
    }
}

public static double product(Object array) {
    double product = 1;
    for (int i = 0, n = Array.getLength(array); i < n; i++)
        product *= ((Number) Array.get(array, i)).doubleValue();
    return product;
}

public static double product2(int... nums) {
    double product = 1;
    for (int i = 0, n = nums.length; i < n; i++)
        product *= nums[i];
    return product;
}

prints

Took 0.016 seconds to take the product of 10,000,000 ints using an int[].
Took 0.849 seconds to take the product of 10,000,000 ints using reflections.

If you are only working on relatively small arrays, the generic but less efficient solution may be fast enough.