MergeSort实现上的ClassCastException

Question

I was implementing the MergeSort algorithm but I am always getting a ClassCastException while converting it from Object . For comparing two values of K , I used the intValue method. Is there any other way to compare them?

import java.util.Arrays;
public class MergeSort {
    private static <K extends Number> K[] sort(K[] s) {
        int n = s.length;
        if (n == 0 || n == 1)
            return null;
        int mid = n / 2;
        if (n % 2 == 0) {
            K[] s1 = (K[]) new Object[n / 2];
            K[] s2 = (K[]) new Object[n / 2];
            for (int i = 0; i < n / 2; i++) {
                s1[i] = s[i];
                s2[i] = s[i + n / 2];
            }
            return merge(sort(s1), sort(s2));
        } else {
            K[] s1 = (K[]) new Object[n / 2];
            K[] s2 = (K[]) new Object[n / 2 + 1];
            for (int i = 0; i < n / 2; i++) {
                s1[i] = s[i];
                s2[i] = s[i + n / 2];
            }
            s2[n / 2] = s[n - 1];
            return merge(sort(s1), sort(s2));
        }
    }

    private static <K extends Number> K[] merge(K[] s1,K[] s2){
        int ll, rl;
        ll = s1.length;
        rl = s2.length;
        K[] merge = (K[]) new Object[ll+rl];
        int i = 0, j = 0;
        while (i + j < ll + rl) {
            if (j == rl || (i < ll && (s1[i].intValue() < s2[j].intValue())))
                merge[i + j] = s1[i++];
            else
                merge[i + j] = s1[j++];
        }
        return merge;
    }
}

Answer 1

Regarding the exception:

You are creating arrays of Object in your sort method which you then cast to K .

But casting an array like this doesn't magically turn objects into K instances. Your whole idea how to use generics here doesn't make sense. Try implementing your sort for arrays of Number first.

And: normally you would create these "temp" arrays only in the merge step. Also having temp arrays for the first partitioning of data looks suspiciously like waste of memory.