java - How to sort an array or ArrayList<Point> ASC first by x and then by y?

Question

I just want to use Collections.sort or Arrays.sort to sort a list of points (class Point) by x first and then by y.

I have a class Ponto that implements Comparable like this:

public int compareTo(Ponto obj) {
        Ponto tmp = obj;
        if (this.x < tmp.x) {
            return -1;
        } else if (this.x > tmp.x) {
            return 1;
        }
        return 0;
    }

but now I want to sort by y too after x.

How can I do that by modifying the above code? Or is that a better and "clean" way to do this? I also use to pass this code to C++, in which I've created a structure called Point with a equivalent comparable method.

Answer 1

Replace return 0 by the same comparison algo on this.y and obj.y.

By the way, reassigning to tmp is unnecessary here. The optimized picture can look like:

public int compareTo(Ponto other) {
    if (this.x == other.x) {
        return (this.y < other.y) ? -1 : ((this.y == other.y) ? 0 : 1);
    } else {
        return (this.x < other.x) ? -1 : 1;
    }
}