【Java/排序】将对象列表排序的三种常用方式

对象列表排序是日常操作之一，常见方式有三种（Comparable接口、lamda表达式、Comparator），各有其长，现整理列出以备查。

代码：

package com.hy.lab.sortSamples;

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

public class Test {
    public static void main(String[] args){
        // 1.Emp实现Comparable接口，用Collections.sort进行排序
        List<Emp> ls1=new ArrayList<>();
        ls1.add(new Emp("Douglas",50));
        ls1.add(new Emp("Andy",20));
        ls1.add(new Emp("Bill",30));
        ls1.add(new Emp("Cindy",40));
        Collections.sort(ls1);
        for(Emp e:ls1){
            System.out.println(e);
        }

        System.out.println("---------------------------------------------------");

        // 2.用lamda表达式进行排序,不触动Emp2
        List<Emp2> ls2=new ArrayList<>();
        ls2.add(new Emp2("Cindy",40));
        ls2.add(new Emp2("Douglas",50));
        ls2.add(new Emp2("Andy",20));
        ls2.add(new Emp2("Bill",30));
        ls2.sort((Emp2 a,Emp2 b)->a.getName().compareTo(b.getName()));// 一行流
        for(Emp2 e:ls2){
            System.out.println(e);
        }

        System.out.println("---------------------------------------------------");

        // 3.用Comparator进行排序,不触动Emp3
        List<Emp3> ls3=new ArrayList<>();
        ls3.add(new Emp3("Bill",30));
        ls3.add(new Emp3("Cindy",40));
        ls3.add(new Emp3("Douglas",50));
        ls3.add(new Emp3("Andy",20));
        ls3.sort(new Comparator<Emp3>() {
            @Override
            public int compare(Emp3 a, Emp3 b) {
                return a.getName().compareTo(b.getName());
            }
        });
        for(Emp3 e:ls3){
            System.out.println(e);
        }
    }
}

输出：

Emp name=Andy age=20
Emp name=Bill age=30
Emp name=Cindy age=40
Emp name=Douglas age=50
---------------------------------------------------
Emp2 name=Andy age=20
Emp2 name=Bill age=30
Emp2 name=Cindy age=40
Emp2 name=Douglas age=50
---------------------------------------------------
Emp3 name=Andy age=20
Emp3 name=Bill age=30
Emp3 name=Cindy age=40
Emp3 name=Douglas age=50

下面是三个对象类。

Emp类：

package com.hy.lab.sortSamples;

public class Emp implements Comparable<Emp>{
    private String name;
    private int age;

    public Emp(String name,int age){
        this.name=name;
        this.age=age;
    }

    public String toString(){
        return String.format("Emp name=%s age=%d",name,age);
    }

    public String getName() {
        return name;
    }

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

    @Override
    public int compareTo(Emp o) {
        return this.name.compareTo(o.name);
    }
}

Emp2类：

package com.hy.lab.sortSamples;

public class Emp2 {
    private String name;
    private int age;

    public Emp2(String name, int age){
        this.name=name;
        this.age=age;
    }

    public String toString(){
        return String.format("Emp2 name=%s age=%d",name,age);
    }

    public String getName() {
        return name;
    }

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

Emp3类：

package com.hy.lab.sortSamples;

public class Emp3 {
    private String name;
    private int age;

    public Emp3(String name, int age){
        this.name=name;
        this.age=age;
    }

    public String toString(){
        return String.format("Emp3 name=%s age=%d",name,age);
    }

    public String getName() {
        return name;
    }

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

END