Java is the worst.

README.md

Java is the Worst

All I want to do is sort an array of ints by some arbitrary function, criteria(). This is the the only way I've figured out how to do it in Java.

There's a Python implementation of the same thing, for comparison's sake.

sort_test.py

def criteria(x):
    return x % 2 != 0


def sort_test():
    xs = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    ys = sorted(xs, key=criteria)
    print 'Got expected results?', ys == [2, 4, 6, 8, 10, 1, 3, 5, 7, 9]

if __name__ == '__main__':
    sort_test()

SortTest.java

import java.util.Arrays;
import java.util.Comparator;

public class SortTest {

    static boolean criteria(int x) {
        return x % 2 == 0;
    }

    static void sortTest() {
        int[] xs = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

        // Box up the array into Integer objects
        Integer[] xObjs = new Integer[xs.length];
        for (int i = 0; i < xs.length; i++) {
            xObjs[i] = new Integer(xs[i]);
        }

        // Sort those Integer objects
        Arrays.sort(xObjs, new Comparator<Integer>() {
            public int compare(Integer a, Integer b) {
                boolean evenA = criteria(a);
                boolean evenB = criteria(b);
                if (evenA && evenB) {
                    return 0;
                }
                return evenA ? -1 : 1;
            }
        });

        // Unbox them back into primitive ints
        int[] ys = new int[xObjs.length];
        for (int i = 0; i < xObjs.length; i++) {
            ys[i] = xObjs[i].intValue();
        }

        int[] expected = {2, 4, 6, 8, 10, 1, 3, 5, 7, 9};
        System.out.println("Got expected results? " + Arrays.equals(ys, expected));
    }

    public static void main(String[] args) {
        sortTest();
    }
}