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) */@Overridepublic 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) */@Overridepublic 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) */@Overridepublic 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());}}}