对象比较器：Comparable和Comparator

Posted 2020-07-15 胖头猫

在进行对象数组排序的过程中需要使用到比较器，比较器有两个：Comparable和Comparator

java.lang.Comparable：是在类定义是时候默认实现好的接口，里面提供有一个compareTo()方法用于大小比较

java规定：假如a和b是实现Comparable接口类创建的两个对象，

当a.compareTo(b)<0时，称a小于b;

a.compareTo(b)>0时，称a大于b;

a.compareTo(b)==0时，称a等于b。

java.util.Comparator：需要单独定义一个排序的比较规则类，里面有两个方法compare(),equals()

优先使用Comparable

 

package com.wzy.main;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.TreeSet;

import org.omg.PortableInterceptor.Interceptor;
class People implements Comparable{
    People(String name,int age){
        this.name = name;
        this.age = age;
    }
    private String name;
    private int age;
    public int getAge() {
        return age;
    }
    public String getName() {
        return name;
    }
    @Override
    public String toString() {
        return "name="+name+", age="+age;
    }
    @Override
    public int compareTo(Object o) {
        People p = (People)o;
        return p.age-this.age;
    }
}

//使用Comparator比较器
class PersonComparator implements Comparator {
    @Override
    public int compare(Object one, Object another) {
         return ((People)one).getAge()-((People)another).getAge();
    }
    
}
public class Test01 {
public static void main(String[] args) {
    
    List<People> list = new ArrayList<People>();
    list.add(new People("aaa", 15));
    list.add(new People("bbb", 10));
    list.add(new People("ccc", 16));
    list.add(new People("ddd", 13));
    list.add(new People("eee", 19));
    //Collections.sort(list);//按照age进行排序，使用Comparable
    Collections.sort(list, new PersonComparator());//使用Comparator比较器，按照age进行排序
    Iterator<People> interceptor =  list.iterator();
    while(interceptor.hasNext()){
        System.out.println(interceptor.next());
    }
    
}
}