Why is my simple comparator broken?

Question

I have a class, which I have simplified to this:

final class Thing {
    private final int value;
    public Thing(int value) {
        this.value = value;
          


        

Answer 1

Integer overflow… or more precisely, underflow.

Instead, do an explicit comparison:

private static final Comparator reverse = new Comparator() {
    public int compare(Thing a, Thing b) {
      int av = a.getValue(), bv = b.getValue();
      return (av == bv) ? 0 : ((av < bv) ? -1 : +1);
    }
};

Using subtraction is fine if you are sure that the difference won't "wrap around". For example, when the values in question are constrained to be non-negative.