泛型的排序问题（Collections.sort及Comparable的应用）

一.前言

   java中对泛型(集合类型)排序的问题，主要采用了两张方式一种是对要排序的实体类，实现Comparable接口，另一种方式，Collections集合工具类进行排序。

二.实现Comparable接口方式

package com.shine.demo.test;

import java.io.Serializable;

public class Car implements Serializable, Comparable<Car> {

    /**
     * 序列化版本.
     */
    private static final long serialVersionUID = 5854674665110917200L;

    private Long id;

    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int compareTo(Car car) {
        if(!this.id.equals(car.getId()))
            return this.id.compareTo(car.getId());
        else if(!this.name.equals(car.getName()))
            return this.name.compareTo(car.getName());

        return 0;
    }

    @Override
    public String toString() {
        return "Car的id为：" + this.id + ",名称为：" + this.name;
    }

}

实现了Comparable接口，重写compareTo方法。

三.Collections集合工具

package com.shine.demo.test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

public class Test {

    public static void main(String[] args) {

        Car car = new Car();
        car.setId(1L);
        car.setName("小汽车");

        Car car1 = new Car();
        car1.setId(2L);
        car1.setName("货车");

        Car car2 = new Car();
        car2.setId(3L);
        car2.setName("载客小汽车");

        Car car3 = new Car();
        car3.setId(4L);
        car3.setName("出租车");

        //使用Comparable与Set进行排序
        Set<Car> cars = new TreeSet<Car>();
        cars.add(car);
        cars.add(car3);
        cars.add(car1);
        cars.add(car2);    

        for (Car carInfo : cars) {
            System.out.println(carInfo);
        }

        //常用Collections的sort排序
        List<Car> carList = new ArrayList<Car>();
        carList.add(car);
        carList.add(car3);
        carList.add(car1);
        carList.add(car2);    

        Collections.sort(carList, new Comparator<Car>() {

            @Override
            public int compare(Car car1, Car car2) {
                return (int) (car1.getId() - car2.getId());
            }
        });

        for (Car carInfoList : carList) {
            System.out.println(carInfoList);
        }

    }

}

采用了Collections的sort排序方法，其原理是利用了Comparator的类，进行排序。
结果：