java内部比较器和外部比较器

外部比较器，实现comparator,重写compare，以下例子实现包含对象的集合的排序。排序时调用的函数是collections.sort(list,比较器)。

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

/**
 * @date : 2019/5/24
 */
//外部比较器
class MyCompare implements Comparator<Students> {
    @Override
    public int compare(Students s1,Students s2){
        if (s1.getAge()>s2.getAge()){
            return 1;
        }else if (s1.getAge()==s2.getAge()){
            return 0;
        }else{
            return -1;
        }
    }
}
class Students{
    private int age;
    private String name;

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

    public Students() {
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString(){
    	return "Name:"+name+",Age:"+age;
    }
}
public class TestCompare{
    public static void main(String[] args){
        List<Students> arr = new ArrayList<>();
        arr.add(new Students(20,"mark"));
        arr.add(new Students(22,"kaven"));
        arr.add(new Students(16,"daxia"));
        arr.add(new Students(25,"handoking"));
        Collections.sort(arr,new MyCompare());
        System.out.println(arr.get(1).toStirng);
        }
}

内部比较器就是把比较器定义在内部，这是要实现的接口为comparable,重写compareTo,实现包含实体类对象的集合的排序时，调用的是collections.sort(list).

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

/**
 * @date : 2019/5/24
 */
//内部比较器
class Students implements Comparable<Students> {
    private int age;
    private String name;

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

    public Students() {
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setName(String name) {
        this.name = name;
    }
     @Override
     public int compareTo(Students s1){
         if (this.getAge()>s1.getAge()){
             return 1;
         }else if (this.getAge()==s1.getAge()){
             return 0;
         }else{
             return -1;
         }
     }
    @Override
    public String toString(){
        return "Name:" + name +",Age:"+age;
    }
}
public class TestCompare{
    public static void main(String[] args){
        List<Students> arr = new ArrayList<>();
        arr.add(new Students(20,"mark"));
        arr.add(new Students(22,"kaven"));
        arr.add(new Students(16,"daxia"));
        arr.add(new Students(25,"handoking"));
        Collections.sort(arr);
        System.out.println(arr.get(0).toString());
        }
}