Comparable 与 Comparator

Java 自定义对象不能直接进行比较，需要实现 Comparable 接口或者 Comparator 接口。

1、Comparable 接口

此接口强行对实现它的每个类的对象自进行整体排序。这种排序被称为类的自然排序，类的compareTo 方法被称为它的自然比较方法。

package com.latiny.basic;

import java.util.Arrays;

public class ComparableTest {

    public static void main(String[] args) {

        int[] nums = {4, 3, 2, 1, 5, 6};
        Arrays.sort(nums);
        System.out.println(Arrays.toString(nums));
        
        String[] strs = {"Jack", "Rose", "Mia", "Latiny", "贝贝", "欢欢"};
        Arrays.sort(strs);
        System.out.println(Arrays.toString(strs));
        
        Bird[] cats = {new Bird("Jmy", 4), new Bird("Feign", 1), new Bird("Selina", 9)};
        Arrays.sort(cats);
        System.out.println(Arrays.toString(cats));
    }

}

class Bird implements Comparable<Bird> {
    String name;
    int age;
    
    public Bird() {
        super();
    }

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

    @Override
    public String toString() {
        return "[name:" + name + ", " + "age:" +age + "]";
    }
    
    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;
    }

    @Override
    public int compareTo(Bird bird) {
        return this.age - bird.age;
    }
}

2、Comparator

Comparator 接口是要求自定类去实现，按照OO原则，对修改关闭，对扩展开放。适合类已定义好，不能或者不想再去修改它时，又需要对它进行比较时，通过组合一个新类实现Comparator接口的 compare方法。

public class ComparableTest {

    public static void main(String[] args) {

        Bike[] bikes = {new Bike("Latiny", 20), new Bike("Luise", 30), new Bike("Jordan", 28)};
        Arrays.sort(bikes, new BikeComparator());
        System.out.println(Arrays.toString(bikes));
    }
}

class BikeComparator implements Comparator<Bike> {

    @Override
    public int compare(Bike o1, Bike o2) {
        return o1.getSpeed() - o2.getSpeed();
    }
}

class Bike {
    private String name;
    private int speed;
    
    public Bike(String name, int speed) {
        super();
        this.name = name;
        this.speed = speed;
    }
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getSpeed() {
        return speed;
    }
    public void setSpeed(int speed) {
        this.speed = speed;
    }
    @Override
    public String toString() {
        return "Bike [name=" + name + ", speed=" + speed + "]";
    }
}