Java比较器

一、Comparable接口

类直接实现Comparable接口，并实现compareTo方法

package cn.lxx.test;
 
public class User implements Comparable<User> {   //该类实现Comparable接口，参数为User
    private String name;
    private int age;
    private boolean sex;
 
    public User() {
    }
 
    public User(String name, int age, boolean sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                '}';
    }
 
    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 boolean isSex() {
        return sex;
    }
 
    public void setSex(boolean sex) {
        this.sex = sex;
    }
 
    /**
     * 重写compareTo方法，实现年龄升序,年龄相同则姓名升序
     **/
    @Override
    public int compareTo(User user) {
        if (this.age == user.age) return this.name.compareTo(user.name);
        return this.age - user.age; //将this想像成一排不变的对象(已经按照要求排好序的)，而User就是当前要插入的对象，只有user属性小于this属性才插入从而升序，个人理解，希望有所帮助
    }
}
 
class Test {
    public static void main(String[] args) {
        User user1 = new User("ake", 25, true);
        User user2 = new User("reo", 24, false);
        User user3 = new User("fg", 24, false);
        List<User> list = new ArrayList<User>();
        list.add(user1);
        list.add(user2);
        list.add(user3);
        Collections.sort(list);
        System.out.println("Comparable:" + list);
    }
}

二、Comparator接口

两种方式：一种是类直接实现接口，并实现compare方法（不推荐，强耦合）；另一种是匿名内部类实现接口，并实现compare方法。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
 
public class User implements Comparator<User> {
    private String name;
    private int age;
    private boolean sex;
 
    public User() {
    }
 
    public User(String name, int age, boolean sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                '}';
    }
 
    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 boolean isSex() {
        return sex;
    }
 
    public void setSex(boolean sex) {
        this.sex = sex;
    }
 
    @Override
    public int compare(User o1, User o2) {
        return o1.age-o2.age;
    }
}
class Test{
    public static void main(String[] args) {
        User user1=new User("dingli",25,true);
        User user2=new User("huxiaojuan",24,false);
        User user3=new User("xxx",24,false);
        List<User> list=new ArrayList<User>();
        list.add(user1);
        list.add(user2);
        list.add(user3);

      	// 方式1：
        Collections.sort(list, new User()); //类实现了的Comparator能满足需求
        System.out.println("类自身实现Comparator:"+list);

        // 方式2：
				Collections.sort(list, new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                return o1.getName().compareTo(o2.getName()); //按照名字升序
            }
        });
        System.out.println("匿名内部类方式："+list);

    }
}

三、比较两个接口

Comparable是内比较器，Comparator是外比较器。即实现Comparable接口的类，具备对象之间的直接比较；实现Comparator接口的类，不具备对象之间的直接比较。

public static <T extends Comparable<? super T>> void sort(List<T> list) 
public static <T> void sort(List<T> list, Comparator<? super T> c)