Comparator and Comparable in Java

1. java.lang.Comparable
   java.util.Comparator

2. Comparable enables you to compare and how to compare.
   Comparator can change the way to compare.

3.
@Override// for Comparable
public int compareTo(T o) { }

@Override// for Comparator
public int compare(T o1, T o2) { }

4. 实例

package com.eric.essential;

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;

public class COMPARABLE implements Comparable<COMPARABLE> {
 private int x;
 private int y;
 public COMPARABLE(int x, int y){
  this.x = x;
  this.y = y;
 }
 
 @Override
 public String toString() {
  return "(" + x + "," + y + ")";
 }
 @Override
 public int compareTo(COMPARABLE o) {
  return x > o.getX() ? 1 : (x == o.getX() ? 0 : -1);
 }
 public int getX() {
  return x;
 }
 public int getY() {
  return y;
 }
 
 public static void main(String[] args) {

  Comparator<COMPARABLE> comp = new Comparator<COMPARABLE>(){
   public int compare(COMPARABLE o1, COMPARABLE o2) {
    return o1.getY() > o2.getY() ? 1 :(o1.getY() == o2.getY() ? 0 : -1);
   }
  };

  COMPARABLE[] test = {
    new COMPARABLE(9,19),new COMPARABLE(10,10),
    new COMPARABLE(1,1),new COMPARABLE(2,21),
    new COMPARABLE(5,51),new COMPARABLE(6,16),
    new COMPARABLE(7,17),new COMPARABLE(8,18),
    new COMPARABLE(3,31),new COMPARABLE(4,41),
    new COMPARABLE(11,11),new COMPARABLE(12,12)};
  
  System.out.println("Before Sort()");
  System.out.println(Arrays.toString(test));
  
  Arrays.sort(test);
  System.out.println("After  Sort()");
  System.out.println(Arrays.toString(test));
  
  Arrays.sort(test, Collections.reverseOrder());
  System.out.println("After Reverse Sort()");
  System.out.println(Arrays.toString(test));
  
  System.out.println("After COMPARATOR Sort");
  Arrays.sort(test, comp);
  System.out.println(Arrays.toString(test));
  
 }
}

结果：
Before Sort()
[(9,19), (10,10), (1,1), (2,21), (5,51), (6,16), (7,17), (8,18), (3,31), (4,41), (11,11), (12,12)]
After  Sort()
[(1,1), (2,21), (3,31), (4,41), (5,51), (6,16), (7,17), (8,18), (9,19), (10,10), (11,11), (12,12)]
After Reverse Sort()
[(12,12), (11,11), (10,10), (9,19), (8,18), (7,17), (6,16), (5,51), (4,41), (3,31), (2,21), (1,1)]
After COMPARATOR Sort
[(1,1), (10,10), (11,11), (12,12), (6,16), (7,17), (8,18), (9,19), (2,21), (3,31), (4,41), (5,51)]