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Comparable接口和Comparator接口

时间:2018-08-18 23:36:12      阅读:182      评论:0      收藏:0      [点我收藏+]

标签:简单的   对象   err   lang   vat   ted   sys   string   实例   

 这两个接口经常容易混淆,不用的时候不清楚,用的时候就很容易出错,现摘抄网络上的一篇清楚的文章在此,便于日后查阅。

 

 

在实际应用中,我们往往有需要比较两个自定义对象大小的地方。而这些自定义对象的比较,就不像简单的整型数据那么简单,它们往往包含有许多的属性,我们一般都是根据这些属性对自定义对象进行比较的。所以Java中要比较对象的大小或者要对对象的集合进行排序,需要通过比较这些对象的某些属性的大小来确定它们之间的大小关系。

一般,Java中通过接口实现两个对象的比较,比较常用就是Comparable接口和Comparator接口。首先类要实现接口,并且使用泛型规定要进行比较的对象所属的类,然后类实现了接口后,还需要实现接口定义的比较方法(compareTo方法或者compare方法),在这些方法中传入需要比较大小的另一个对象,通过选定的成员变量与之比较,如果大于则返回1,小于返回-1,相等返回0。

一、Comparable接口

1.什么是Comparable接口

此接口强行对实现它的每个类的对象进行整体排序。此排序被称为该类的自然排序 ,类的 compareTo方法被称为它的自然比较方法 。实现此接口的对象列表(和数组)可以通过 Collections.sort(和 Arrays.sort )进行自动排序。实现此接口的对象可以用作有序映射表中的键或有序集合中的元素,无需指定比较器。 

2.实现什么方法

int compareTo(T o)

比较此对象与指定对象的顺序。如果该对象小于、等于或大于指定对象,则分别返回负整数、零或正整数。

参数: o - 要比较的对象。

返回:负整数、零或正整数,根据此对象是小于、等于还是大于指定对象。

抛出:ClassCastException - 如果指定对象的类型不允许它与此对象进行比较。

3.实例

package com.mxl.algorithlm;

import java.util.Date;
/**
 * 因为要实现对ConsumInfo对象的排序,所以在ConsunInfo类中要实现Comparable接口,也就是要实现compareTo()方法
 * 具体的比较参照:依次按照price、uid进行倒序排序
 * @author breeze
 *
 */
public class ConsumInfo implements Comparable<ConsumInfo> {
    private int uid;
    private String name;
    private double price;
    private Date datetime;
    
    public ConsumInfo() {
        // TODO Auto-generated constructor stub
    }
    
    public ConsumInfo(int uid,String name,double price,Date datetime){
        this.uid = uid;
        this.name = name;
        this.price = price;
        this.datetime = datetime;
                
    }
    
    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public Date getDatetime() {
        return datetime;
    }

    public void setDatetime(Date datetime) {
        this.datetime = datetime;
    }
    

    @Override
    public String toString() {
        return "ConsumInfo [uid=" + uid + ", name=" + name + ", price=" + price
                + ", datetime=" + datetime + "]";
    }
    /**
     * 这里比较的是什么, Collections.sort方法实现的就是按照此比较的东西排列
     * 顺序(从小到大):
     * if(price < o.price){
            return -1;
        }
        if(price > o.price){
            return 1;
        }
     * 倒序(从大到小):
     * if(price < o.price){
            return 1;
        }
        if(price > o.price){
            return -1;
        }
     * 
     */
    @Override
    public int compareTo(ConsumInfo o) {
        //首先比较price,如果price相同,则比较uid
        if(price < o.price){
            return -1;
        }
        if(price > o.price){
            return 1;
        }
        
        if(price == o.price){
            if(uid < o.uid){
                return -1;
            }
            if(uid > o.uid){
                return 1;
            }
        }
        return 0;
    }
    
    
}

//测试类

package com.mxl.algorithlm;

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

public class ConsumInfoTest {
    
    public static void main(String[] args) {
        
        ConsumInfo consumInfo1 = new ConsumInfo(100, "consumInfo1", 400.0,new Date());
        ConsumInfo consumInfo2 = new ConsumInfo(200, "consumInfo1", 200.0,new Date());
        ConsumInfo consumInfo3 = new ConsumInfo(300, "consumInfo1", 100.0,new Date());
        ConsumInfo consumInfo4 = new ConsumInfo(400, "consumInfo1", 700.0,new Date());
        ConsumInfo consumInfo5 = new ConsumInfo(500, "consumInfo1", 800.0,new Date());
        ConsumInfo consumInfo6 = new ConsumInfo(600, "consumInfo1", 300.0,new Date());
        ConsumInfo consumInfo7 = new ConsumInfo(700, "consumInfo1", 900.0,new Date());
        ConsumInfo consumInfo8 = new ConsumInfo(800, "consumInfo1", 400.0,new Date());
        
        List<ConsumInfo> list = new ArrayList<ConsumInfo>();
        list.add(consumInfo1);
        list.add(consumInfo2);
        list.add(consumInfo3);
        list.add(consumInfo4);
        list.add(consumInfo5);
        list.add(consumInfo6);
        list.add(consumInfo7);
        list.add(consumInfo8);
        System.out.println("排序前:");
        //排序前
        for(ConsumInfo consumInfo : list ){
            System.out.println(consumInfo);
        }
        
        Collections.sort(list);//排序
        System.out.println("排序后:");
        //排序后
        for(ConsumInfo consumInfo :list){
            System.out.println(consumInfo);
        }
    }
}

二、Comparator接口

与上面的Comparable接口不同的是:

①、Comparator位于包java.util下,而Comparable位于包java.lang下。

②、Comparable接口将比较代码嵌入需要进行比较的类的自身代码中,而Comparator接口在一个独立的类中实现比较。

③、如果前期类的设计没有考虑到类的Compare问题而没有实现Comparable接口,后期可以通过Comparator接口来实现比较算法进行排序,并且为了使用不同的排序标准做准备,比如:升序、降序。

④、Comparable接口强制进行自然排序,而Comparator接口不强制进行自然排序,可以指定排序顺序。

使用实例:

 

package test;

import java.util.Comparator;
/**
 * 具体的比较类(比较器),实现Comparator接口
 * @author breeze
 *
 */
public class ComparatorConsunInfo implements Comparator<ConsumInfo> {
    /**
     * 顺序(从小到大):
     * if(price < o.price){
            return -1;
        }
        if(price > o.price){
            return 1;
        }
     * 倒序(从大到小):
     * if(price < o.price){
            return 1;
        }
        if(price > o.price){
            return -1;
        }
     */
    @Override
    public int compare(ConsumInfo o1, ConsumInfo o2) {
         //首先比较price,如果price相同,则比较uid
        if(o1.getPrice() > o2.getPrice()){
            return 1;
        }
        
        if(o1.getPrice() < o2.getPrice()){
            return -1;
        }
        
        if(o1.getPrice() == o2.getPrice()){
            if(o1.getUid() > o2.getUid()){
                return 1;
            }
            if(o1.getUid() < o2.getUid()){
                return -1;
            }
        }
        return 0;
    }

}


/**
 * 需要进行比较的类
 * @author breeze
 *
 */
public class ConsumInfo{
    private int uid;
    private String name;
    private double price;
    private Date datetime;
    
    public ConsumInfo() {
        // TODO Auto-generated constructor stub
    }
    
    public ConsumInfo(int uid,String name,double price,Date datetime){
        this.uid = uid;
        this.name = name;
        this.price = price;
        this.datetime = datetime;
                
    }
    
    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public Date getDatetime() {
        return datetime;
    }

    public void setDatetime(Date datetime) {
        this.datetime = datetime;
    }

    @Override
    public String toString() {
        return "ConsumInfo [uid=" + uid + ", name=" + name + ", price=" + price
                + ", datetime=" + datetime + "]";
    }
    
}


//测试类
public class ConsumInfoTest {
    
    public static void main(String[] args) {
        
        ConsumInfo consumInfo1 = new ConsumInfo(100, "consumInfo1", 400.0,new Date());
        ConsumInfo consumInfo2 = new ConsumInfo(200, "consumInfo1", 200.0,new Date());
        ConsumInfo consumInfo3 = new ConsumInfo(300, "consumInfo1", 100.0,new Date());
        ConsumInfo consumInfo4 = new ConsumInfo(400, "consumInfo1", 700.0,new Date());
        ConsumInfo consumInfo5 = new ConsumInfo(500, "consumInfo1", 800.0,new Date());
        ConsumInfo consumInfo6 = new ConsumInfo(600, "consumInfo1", 300.0,new Date());
        ConsumInfo consumInfo7 = new ConsumInfo(700, "consumInfo1", 900.0,new Date());
        ConsumInfo consumInfo8 = new ConsumInfo(800, "consumInfo1", 400.0,new Date());
        
        List<ConsumInfo> list = new ArrayList<ConsumInfo>();
        list.add(consumInfo1);
        list.add(consumInfo2);
        list.add(consumInfo3);
        list.add(consumInfo4);
        list.add(consumInfo5);
        list.add(consumInfo6);
        list.add(consumInfo7);
        list.add(consumInfo8);
        
        System.out.println("排序前:");
        //排序前
        for(ConsumInfo consumInfo : list ){
            System.out.println(consumInfo);
        }
        ComparatorConsunInfo comparatorConsunInfo = new ComparatorConsunInfo();//比较器
        Collections.sort(list,comparatorConsunInfo);//排序
        System.out.println("排序后:");
        //排序后
        for(ConsumInfo consumInfo :list){
            System.out.println(consumInfo);
        }
    }
}
package test;

import java.util.Comparator;
/**
 * 具体的比较类(比较器),实现Comparator接口
 * @author breeze
 *
 */
public class ComparatorConsunInfo implements Comparator<ConsumInfo> {
    /**
     * 顺序(从小到大):
     * if(price < o.price){
            return -1;
        }
        if(price > o.price){
            return 1;
        }
     * 倒序(从大到小):
     * if(price < o.price){
            return 1;
        }
        if(price > o.price){
            return -1;
        }
     */
    @Override
    public int compare(ConsumInfo o1, ConsumInfo o2) {
         //首先比较price,如果price相同,则比较uid
        if(o1.getPrice() > o2.getPrice()){
            return 1;
        }
        
        if(o1.getPrice() < o2.getPrice()){
            return -1;
        }
        
        if(o1.getPrice() == o2.getPrice()){
            if(o1.getUid() > o2.getUid()){
                return 1;
            }
            if(o1.getUid() < o2.getUid()){
                return -1;
            }
        }
        return 0;
    }

}


/**
 * 需要进行比较的类
 * @author breeze
 *
 */
public class ConsumInfo{
    private int uid;
    private String name;
    private double price;
    private Date datetime;
    
    public ConsumInfo() {
        // TODO Auto-generated constructor stub
    }
    
    public ConsumInfo(int uid,String name,double price,Date datetime){
        this.uid = uid;
        this.name = name;
        this.price = price;
        this.datetime = datetime;
                
    }
    
    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public Date getDatetime() {
        return datetime;
    }

    public void setDatetime(Date datetime) {
        this.datetime = datetime;
    }

    @Override
    public String toString() {
        return "ConsumInfo [uid=" + uid + ", name=" + name + ", price=" + price
                + ", datetime=" + datetime + "]";
    }
    
}


//测试类
public class ConsumInfoTest {
    
    public static void main(String[] args) {
        
        ConsumInfo consumInfo1 = new ConsumInfo(100, "consumInfo1", 400.0,new Date());
        ConsumInfo consumInfo2 = new ConsumInfo(200, "consumInfo1", 200.0,new Date());
        ConsumInfo consumInfo3 = new ConsumInfo(300, "consumInfo1", 100.0,new Date());
        ConsumInfo consumInfo4 = new ConsumInfo(400, "consumInfo1", 700.0,new Date());
        ConsumInfo consumInfo5 = new ConsumInfo(500, "consumInfo1", 800.0,new Date());
        ConsumInfo consumInfo6 = new ConsumInfo(600, "consumInfo1", 300.0,new Date());
        ConsumInfo consumInfo7 = new ConsumInfo(700, "consumInfo1", 900.0,new Date());
        ConsumInfo consumInfo8 = new ConsumInfo(800, "consumInfo1", 400.0,new Date());
        
        List<ConsumInfo> list = new ArrayList<ConsumInfo>();
        list.add(consumInfo1);
        list.add(consumInfo2);
        list.add(consumInfo3);
        list.add(consumInfo4);
        list.add(consumInfo5);
        list.add(consumInfo6);
        list.add(consumInfo7);
        list.add(consumInfo8);
        
        System.out.println("排序前:");
        //排序前
        for(ConsumInfo consumInfo : list ){
            System.out.println(consumInfo);
        }
        ComparatorConsunInfo comparatorConsunInfo = new ComparatorConsunInfo();//比较器
        Collections.sort(list,comparatorConsunInfo);//排序
        System.out.println("排序后:");
        //排序后
        for(ConsumInfo consumInfo :list){
            System.out.println(consumInfo);
        }
    }
}

 

Comparable接口和Comparator接口

标签:简单的   对象   err   lang   vat   ted   sys   string   实例   

原文地址:https://www.cnblogs.com/jiliunyongjin/p/9499044.html

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