Java hashCode 不适用于 HashMap?

I'm attempting to implement a sparse grid using HashMap, however it seems that overriding hashCode() doesn't work quite how I expect. I've boiled down my issue to the following code:

public class Main {

private static class Coord {
    int x, y;

    public Coord(int x, int y) {
        this.x = x;
        this.y = y;
        }

        @Override
        public int hashCode() {
            // See https://en.wikipedia.org/wiki/Pairing_function#Cantor_pairing_function
            return (((x + y) * (x + y + 1)) / 2) + y;
        }
    }

    public static void main(String[] args) {
        HashMap<Coord, String> grid = new HashMap<Coord, String>();
        grid.put(new Coord(0, 0), "A");
        System.out.println(grid.get(new Coord(0, 0)));
    }
}

我希望输出是:

A

但是，输出是:

null

两个new Coord(0, 0)"实例都应该返回相同的 hashCode()，但它似乎不像我预期的那样工作.为什么它没有按我的预期工作?