public final Comparator<Point> SLOPE_ORDER

Question

I have to implement an API which has a "comparator".But I don't know what it is and how to make it.Please help.Here is my API:

public class Point implements Comparable<Point> {
     public final Comparator<Point> SLOPE_ORDER;        // compare points by slope to   this point

     public Point(int x, int y)                         // construct the point (x, y)

     public   void draw()                               // draw this point
     public   void drawTo(Point that)                   // draw the line segment from       this point to that point
     public String toString()                           // string representation

     public    int compareTo(Point that)                // is this point lexicographically    smaller than that point?
     public double slopeTo(Point that)                  // the slope between this point and that point

}

What the line"public final Comparator SLOPE_ORDER"mean ? and How to make it?

Here is my code:

/*************************************************************************
 * Name:
 * Email:
 *
 * Compilation:  javac Point.java
 * Execution:
 * Dependencies: StdDraw.java
 *
 * Description: An immutable data type for points in the plane.
 *
 *************************************************************************/

import java.util.Comparator;

public class Point implements Comparable<Point> {

// compare points by slope
public final Comparator<Point> SLOPE_ORDER;       // YOUR DEFINITION HERE

private final int x;                              // x coordinate
private final int y;                              // y coordinate

// create the point (x, y)
public Point(int x, int y) {
    /* DO NOT MODIFY */
    this.x = x;
    this.y = y;
}

// plot this point to standard drawing
public void draw() {
    /* DO NOT MODIFY */
    StdDraw.point(x, y);
}

// draw line between this point and that point to standard drawing
public void drawTo(Point that) {
    /* DO NOT MODIFY */
    StdDraw.line(this.x, this.y, that.x, that.y);
}

// slope between this point and that point
public double slopeTo(Point that) {
    /* YOUR CODE HERE */
    double slope = (that.y*1.0-this.y)/(that.x*1.0-this.x);
    return slipe;
}

// is this point lexicographically smaller than that one?
// comparing y-coordinates and breaking ties by x-coordinates
public int compareTo(Point that) {
    /* YOUR CODE HERE */
    if(this.y<that.y) return 1;
    else if(this.y==that.y) {
        if(this.x<that.x) return 1;
        else return 0;
    }
    else return 0;
} 

// return string representation of this point
public String toString() {
    /* DO NOT MODIFY */
    return "(" + x + ", " + y + ")";
}

// unit test
public static void main(String[] args) {
    /* YOUR CODE HERE */
}
}

Answer 1

Something like this

public final Comparator<Point> SLOPE_ORDER = new Comparator<Point>()
{
    @Override
    public int compare(Point p0, Point p1)
    {
        double s0 = slopeTo(p0);
        double s1 = slopeTo(p1);
        return Double.compare(s0, s1);
    }
};