How To Sort Objects With Java Interface Comparable and Comparator

Java 提供了Comparable 和Comparator 两个接口让程序员可以实现Java对象的排序。

首先总结下Comparable 与Comparator接口的区别：

java.lang.Comparable	java.util.Comparator
int objOne.compareTo(objTwo)	int compare (objOne, objTwo)
返回： 负数: 如果 objOne < objTwo 零: 如果 objOne == objTwo 正数: 如果 objOne > objTwo	同 Comparable
必须修改要比较的类的结构，令其实现Comparable 接口	编写一个独立的类，令其实现Comparator接口
一个类只能有一种排序	一个类可以有多重排序方式，只要多编写一个Comparator的实现类就好了。
JAVA API中经常用到，例如：String, 包装类（Integer, Long, Double…）, Date, Calendar …	用于对第三方类的排序，因为第三方类一般都是无法修改的，更别说实现Comparable了，所以只能使用Comparator了。

Comparable 实现对象方式：

package com.citi.crc;

public class AudiCar implements Comparable<AudiCar> {

private String series;
private Double price;
private Double speed;

public String getSeries() {
return series;
}

public void setSeries(String series) {
this.series = series;
}

public Double getPrice() {
return price;
}

public void setPrice(Double price) {
this.price = price;
}

public Double getSpeed() {
return speed;
}

public void setSpeed(Double speed) {
this.speed = speed;
}

/* (non-Javadoc)
* @see java.lang.Comparable#compareTo(java.lang.Object)
*/
@Override
public int compareTo(AudiCar o) {
return this.getPrice().compareTo(o.getPrice());
}
}

package com.citi.crc;

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

public class TestAudiCar {

public static void main(String[] args) {
List<AudiCar> cars = new ArrayList<AudiCar>();

AudiCar audiA3 = new AudiCar();
audiA3.setSeries("A3");
audiA3.setPrice(200000d);
audiA3.setSpeed(80d);

AudiCar audiA4 = new AudiCar();
audiA4.setSeries("A4");
audiA4.setPrice(260000d);
audiA4.setSpeed(90d);

AudiCar audiA6 = new AudiCar();
audiA6.setSeries("A6");
audiA6.setPrice(320000d);
audiA6.setSpeed(100d);

cars.add(audiA4);
cars.add(audiA6);
cars.add(audiA3);

Collections.sort(cars);
//		Collections.reverse(cars);
for (AudiCar car : cars) {
System.out.println(car.getPrice());
}
}
}

Comparator 实现排序方式：

package com.citi.crc;

import java.util.Comparator;

public class AudiCar {

private String series;
private Double price;
private Double speed;

public String getSeries() {
return series;
}

public void setSeries(String series) {
this.series = series;
}

public Double getPrice() {
return price;
}

public void setPrice(Double price) {
this.price = price;
}

public Double getSpeed() {
return speed;
}

public void setSpeed(Double speed) {
this.speed = speed;
}

static class PriceComparator implements Comparator<AudiCar> {

/* (non-Javadoc)
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
@Override
public int compare(AudiCar o1, AudiCar o2) {
return o1.getPrice().compareTo(o2.getPrice());
}

}

static class SpeedComparator implements Comparator<AudiCar> {
/* (non-Javadoc)
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
@Override
public int compare(AudiCar o1, AudiCar o2) {
return o1.getSpeed().compareTo(o2.getSpeed());
}
}
}

package com.citi.crc;

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

public class TestAudiCar {

public static void main(String[] args) {
List<AudiCar> cars = new ArrayList<AudiCar>();

AudiCar audiA3 = new AudiCar();
audiA3.setSeries("A3");
audiA3.setPrice(200000d);
audiA3.setSpeed(80d);

AudiCar audiA4 = new AudiCar();
audiA4.setSeries("A4");
audiA4.setPrice(260000d);
audiA4.setSpeed(90d);

AudiCar audiA6 = new AudiCar();
audiA6.setSeries("A6");
audiA6.setPrice(320000d);
audiA6.setSpeed(100d);

cars.add(audiA4);
cars.add(audiA6);
cars.add(audiA3);

Collections.sort(cars, new AudiCar.PriceComparator());
//		Collections.sort(cars, new AudiCar.SpeedComparator());

for (AudiCar car : cars) {
System.out.println(car.getPrice());
}
}
}