public class Coord2 implements Comparable {
    final int x, y;
    public Coord2(int x, int y) {
        this.x = x;
        this.y = y;
    }
    /**
     * Compares by the x-coordinate first. If that
     * is equal, it compares the y-coordinate.
     */
    @Override
    public int compareTo(Object obj) {
        Coord2 that = (Coord2)obj;
        int diff = 0;
        if(diff == 0) diff = this.x - that.x;
        if(diff == 0) diff = this.y - that.y;
        return diff;
    }
}