Puzzle 59 – Comparing the Java way.

A really cool part of the collection framework is the Collections.sort() function. The function sorts out a collection based on the natural ordering of elements. Of course – for you own data types you need to define what the ‘natural’ ordering is. Doing that is really simple though – just implement the compareTo() method of the Comparable interface and we are ready to go.

That brings me to today’s questions. The code below for the Points class implements the compareTo() method. Now my manager kept insisting that there is something not right about it – but the code looks alright to me.

What do you folks think – are there any problems with the code below?

package com.twister;

import java.util.ArrayList;
import java.util.Collections;

public class Points implements Comparable<Points>{
int xCoordinate;
/*
* 1. Returns 0 if both points have same xCoordinate (say 3 & 3) - returns 3-3=0
* 2. Returns +ve if first point is on the
* right hand side of the second point (say 5, -3) - returns 5 - (-3) = 8
* 3. Returns -ve if first point is on the
* left hand side of the second point (say -5, 3) - returns (-5) - (3) = -8
*/
public int compareTo(Points p) {
   return xCoordinate - p.xCoordinate;
};

public static void main(String[] args) {
   ArrayList<Points> arrPoints = new ArrayList<Points>();
   /* Add lots of points to the array list */
   Collections.sort(arrPoints);
   /*Print the sorted collection */
}
}

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