一、比较器

在Java中对基本类型进行排序可以通过Array.sort()和Collections.sort()，默认是升序
在Java中对对象进行排序可以通过Compare和CompareTo，并且也可以对基本数据类型进行排序

注意：如果想要对自定义类进行排序，需要重写CompareTo或Compare方法

1、Compare

Compare是Comparator接口中的一个方法，用于比较对象和对象的顺序【对象排序】

compare方法：

int compare(T o1,T o2)

CompareTo方法返回一个int类型的数据
如果该对象小于指定对象，返回负整数
如果该对象等于指定对象，返回0
如果该对象大于指定对象，返回正整数

代码案例：

package cn.com.example11;

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


public class Student implements Comparator<Student> {

    private int id;

    private String name;

    private int age;

    private String sex;

    public Student() {
    }

    public Student(int id, String name, int age, String sex) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public int getId() {
        return id;
    }

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

    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 String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }


    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }

    @Override
    public int compare(Student o1, Student o2) {
        if(o1.getAge() - o2.getAge() == 0){

            return o1.getName().compareTo(o2.getName());
        }
        return o1.getAge() - o2.getAge();
    }

    public static void main(String[] args) {

        List<Student> list = new ArrayList<>();
        list.add(new Student(1,"张三",20,"男"));
        list.add(new Student(2,"李四",21,"女"));
        list.add(new Student(3,"王五",19,"女"));
        list.add(new Student(4,"赵六",19,"男"));
        list.add(new Student(5,"田七",18,"男"));


        // 排序
        Collections.sort(list,new Student());

        for (Student student : list) {
            System.out.println(student);
        }



    }
}

2、CompareTo

CompareTo是Comparable接口中的一个方法，用于比较对象和对象的顺序【对象排序】

compareTo方法：

int compareTo(T o)

CompareTo方法返回一个int类型的数据
如果该对象小于指定对象，返回负整数
如果该对象等于指定对象，返回0
如果该对象大于指定对象，返回正整数

代码案例：

package cn.com.example11;

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

public class Student implements Comparable<Student>{

    private int id;

    private String name;

    private int age;

    private String sex;

    public Student() {
    }

    public Student(int id, String name, int age, String sex) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public int getId() {
        return id;
    }

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

    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 String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }


    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }

    @Override
    public int compareTo(Student o) {
        // 年龄从小到大排序，如果相等通过姓名排序

        if(this.getAge() - o.getAge() == 0){
            return this.getName().compareTo(o.getName());
        }

        return this.getAge() - o.getAge();
    }


    public static void main(String[] args) {

        List<Student> list = new ArrayList<>();
        list.add(new Student(1,"张三",20,"男"));
        list.add(new Student(2,"李四",21,"女"));
        list.add(new Student(3,"王五",19,"女"));
        list.add(new Student(4,"赵六",19,"男"));
        list.add(new Student(5,"田七",18,"男"));


        // 排序
        Collections.sort(list);

        for (Student student : list) {
            System.out.println(student);
        }



    }
}