Chapter 20

import java.util.*;

public class SortPoints {

    public static void main(String[] args) {

        Point[] points = new Point[100];
        for (int i = 0; i < points.length; i++) {
            points[i] = new Point(Math.random() * 100, Math.random() * 100);
        }

        System.out.println("Points sorted on x-coordinates: ");
        Arrays.sort(points); 
        for (int i = 0; i < points.length; i++) {
            System.out.println(points[i]);
        }

        System.out.println("\nPoints sorted on y-coordinates: ");
        Arrays.sort(points, new CompareY()); //sort method is invoked to sort points using a comparator
        for (int i = 0; i < points.length; i++) {
            System.out.println(points[i]);
        }
    }
}

class Point implements Comparable<Point> {

    double x;
    double y;

    Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public int compareTo(Point k) { //compares the x coordinates, k is short for key
        if (x == k.x) { //if two points have the same x coordinate, compare their y coordinates
            if (y > k.y) {
                return 1;
            } else if (y < k.y) {
                return -1;
            } else {
                return 0;
            }
        } else if (x > k.x) {
            return 1;
        } else {
            return -1;
        }
    }

    public String toString() { //prints out the points in (x, y) format
        return "(" + x + ", " + y + ")";
    }
}

class CompareY implements Comparator<Point> { //compares two points on their y-coordinates

    @Override
    public int compare(Point k1, Point k2) { //comparator method
        if (k1.y == k2.y) { //if two points have the same y coordinate, compare their x coordinates
            if (k1.x > k2.x) {
                return 1;
            } else if (k1.x < k1.x) {
                return -1;
            } else {
                return 0;
            }
        } else if (k1.y > k2.y) {
            return 1;
        } else {
            return -1;
        }
    }
}