Java Point2D 的比较器不起作用

Question

I have an array of 2D points in Java and want to sort it. I have used comparators from different websites, like for example from Collections.sort doesn't work on List<Point2D.Double> but none of them work for me.

If I for example use the following code:

Point2D[] points = new Point2D[numPoints];
// add some points

Collections.sort(points, new Comparator<Point2D.Double>() {
                public int compare(Point2D.Double p1, Point2D.Double p2) {
                    return (int)(p1.getX() - p2.getX());
                }
            });

I always get the following error message:

error: no suitable method found for sort(Point2D[],<anonymous Comparator<Double>>)
                        Collections.sort(points, new Comparator<Point2D.Double>() {
                                   ^
    method Collections.<T#1>sort(List<T#1>) is not applicable
      (cannot infer type-variable(s) T#1
        (actual and formal argument lists differ in length))
    method Collections.<T#2>sort(List<T#2>,Comparator<? super T#2>) is not applicable
      (cannot infer type-variable(s) T#2
        (argument mismatch; Point2D[] cannot be converted to List<T#2>))
  where T#1,T#2 are type-variables:
    T#1 extends Comparable<? super T#1> declared in method <T#1>sort(List<T#1>)
    T#2 extends Object declared in method <T#2>sort(List<T#2>,Comparator<? super T#2>)
1 error

Is there any obvious reason for that?

Answer 1

You have an array ...[] hence you need Arrays.sort , not Collections.sort which is for any Collection like List.

Arrays.sort(points,
    Comparator.comparingDouble(Point2D::getX)
              .thenComparingDouble(Point2D::getY));

Furthermore Comparator has nice methods for (several) comparing fields.