根据对象的属性，对集合（list / set）中的对象进行排序

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一：针对list

     通过java.util.Collections的sort方法，有2个参数，第一个参数是list对象，第二个参数是new Comparator<对象类>（）{}方法，这个方法实现了compare（）方法，具体代码如下所示：

package com.example.mylearngit;

import com.example.mylearngit.bean.Student;

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

/**
 * Created by YuShuangPing on 2018/11/27.
 */
public class ListSort {
    public static void main(String[] args){
        List<Student>studentList=new ArrayList<Student>();
        studentList.add(new Student(90,"4"));
        studentList.add(new Student(90,"3"));
        studentList.add(new Student(85,"1"));
        studentList.add(new Student(88,"2"));
        Collections.sort(studentList, new Comparator<Student>() {
            @Override
            public int compare(Student t1, Student t2) {
                if (t1.score>t2.score){
                    return 1;
                }else if (t1.score<t2.score){
                    return -1;
                }else {
                    return t1.order.compareTo(t2.order);// 调用String中的compareTo()方法
                }

            }
        });
        System.out.println(studentList);
    }
}

package com.example.mylearngit.bean;

import android.support.annotation.NonNull;

/**
 * Created by YuShuangPing on 2018/11/27.
 */
public class Student {
    public int score;
    public String order;

    public Student(int score, String order) {
        this.score = score;
        this.order = order;
    }

    @Override
    public String toString() {
        return "Student{" +
                "score=" + score +
                ", order='" + order + '\'' +
                '}';
    }
}

代码执行的结果为：

二：针对set

     要排序的对象所属的类implements  Comparable接口，重写了compareTo（）方法，具体代码如下所示：

package com.example.mylearngit;

import com.example.mylearngit.bean.Person;

import java.util.Set;
import java.util.TreeSet;

/**
 * Created by YuShuangPing on 2018/11/27.
 */
public class SetSort {
    public static void main(String[] args){
        Set<Person>set=new TreeSet<>();
        set.add(new Person(18,"3"));
        set.add(new Person(18,"2"));
        set.add(new Person(16,"4"));
        set.add(new Person(17,"1"));
        System.out.println(set);

    }
}

package com.example.mylearngit.bean;

import android.support.annotation.NonNull;

/**
 * Created by YuShuangPing on 2018/11/27.
 */
public class Person implements Comparable<Person>{
    public int age;
    public String order;

    public Person(int age, String order) {
        this.age = age;
        this.order = order;
    }

    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                ", order='" + order + '\'' +
                '}';
    }

    @Override
    public int compareTo(@NonNull Person person) {
        if (this.age>person.age){
            return 1;
        }else if (this.age<person.age){
            return -1;
        }else {
            return this.order.compareTo(person.order);// 调用String中的compareTo()方法
        }
    }
}

代码执行的结果为：