Java：针对list中存储对象的某一属性进行排序

前言：

针对list中存储的bean类，往往需要针对特定属性进行排序

直接贴代码是好习惯

1.首先写一个简单的测试bean类

public class SortBean {
    private String name;
    private int age;
    private int userId;

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

    public String getName() { return name; }
    public void setName(String name) {this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public int getUserId() { return userId; }
    public void setUserId(int userId) { this.userId = userId; }
}

2.写一个main类函数直接看效果

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

public class SortList {
    public static void main(String[] args) {
        List<SortBean> list = new ArrayList<>();

        SortBean sortBean0 = new SortBean("德玛", 20, 20180001);
        SortBean sortBean1 = new SortBean("寒冰", 18, 20180009);
        SortBean sortBean2 = new SortBean("流浪", 99, 20180002);

        list.add(sortBean0);
        list.add(sortBean1);
        list.add(sortBean2);

        System.out.println("before sort ");
        for (SortBean sortBean : list) {
            System.out.println("name: " + sortBean.getName() + "  age: " + sortBean.getAge());
        }

        Collections.sort(list, new Comparator<SortBean>() {
            @Override
            public int compare(SortBean o1, SortBean o2) {
                if (o1.getAge() - o2.getAge() > 0) { //变成 < 可以变成递减排序
                    return 0;
                } else {
                    return -1;
                }
            }
        });

        System.out.println("after sort ");
        for (SortBean sortBean : list) {
            System.out.println("name: " + sortBean.getName() + "  age: " + sortBean.getAge());
        }
    }
}

3.输出效果

before sort 
name: 德玛  age: 20
name: 寒冰  age: 18
name: 流浪  age: 99
after sort 
name: 寒冰  age: 18
name: 德玛  age: 20
name: 流浪  age: 99

4.结语
其实建议在把内部匿名类变成 lambda 表达式（java 8 开始支持），代码会更加简洁
即：
把下面代码片

Collections.sort(list, new Comparator<SortBean>() {
            @Override
            public int compare(SortBean o1, SortBean o2) {
                if (o1.getAge() - o2.getAge() > 0) {
                    return 0;
                } else {
                    return -1;
                }
            }
        });

替换成

list.sort((o1, o2) -> o1.getAge() - o2.getAge()); //递减排序的话改变减号的两个对象位置

这样的话程序就更加简洁