java比较：Comparable与Comparator

实现集合排序的方法为以下两种：

1.集合中的对象实现Comparable接口，在方法compareTo()中实现比较逻辑

2.新建一个比较器，这个比较器实现Comparator接口，在方法compare()中实现比较逻辑

第一种方法：实现Comparable接口
Person.java代码如下：

package com.compare.bean;

public class Person implements Comparable<Person>{

	private int num;
	
	private int weight;
	
	private int score;
	
	public Person(int num,int weight,int score){
		this.num = num;
		this.weight = weight;
		this.score = score;
	}
	
	public int compareTo(Person o) {
		if(this.score>o.score){
			return 1;
		}else {
				return -1;
		}
	}

	public int getNum() {
		return num;
	}

	public void setNum(int num) {
		this.num = num;
	}

	public int getWeight() {
		return weight;
	}

	public void setWeight(int weight) {
		this.weight = weight;
	}

	public int getScore() {
		return score;
	}

	public void setScore(int score) {
		this.score = score;
	}
	
	public String toString(){
		return "Score: "+score+",Weight: "+weight+",Num: "+num;
	}
}

Test.java代码

package com.compare.test;

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

import com.compare.bean.Person;

public class Test {
	
	public static void main(String[] args) {
		testComparable();
	}
    
    public static void testComparable(){
    	List<Person> persons = new ArrayList<Person>();
    	persons.add(new Person(1,2,3));
    	persons.add(new Person(2,2,3));
    	persons.add(new Person(1,3,4));
    	persons.add(new Person(3,2,3));
    	persons.add(new Person(5,2,3));
    	Collections.sort(persons);
    	if(persons!=null&&persons.size()>0){
    		for(Person person:persons){
    			System.out.println(person);
    			System.out.println("========================");
    		}
    	}
    }

}

运行结果：

Score: 3,Weight: 2,Num: 5
========================
Score: 3,Weight: 2,Num: 3
========================
Score: 3,Weight: 2,Num: 2
========================
Score: 3,Weight: 2,Num: 1
========================
Score: 4,Weight: 3,Num: 1
========================

第二种方法：实现Comparator接口
Step.java代码如下：

package com.compare.bean;

public class Step {
	
	private String acceptTime = "";
	
	private String acceptAddress = "";
	
	public Step(){
		super();
	}
	
	public Step(String acceptTime,String acceptAddress){
		this.acceptTime = acceptTime;
		this.acceptAddress = acceptAddress;
	}

	public String getAcceptTime() {
		return acceptTime;
	}

	public void setAcceptTime(String acceptTime) {
		this.acceptTime = acceptTime;
	}

	public String getAcceptAddress() {
		return acceptAddress;
	}

	public void setAcceptAddress(String acceptAddress) {
		this.acceptAddress = acceptAddress;
	}
	
}

StepComparator.java代码如下：

package com.compare.util;

import java.util.Comparator;
import java.util.Date;

import com.compare.bean.Step;

public class StepComparator implements Comparator<Step>{

	public int compare(Step o1, Step o2) {
		Date acceptTime1 = UtilTool.strToDate(o1.getAcceptTime(), "yyyy-MM-dd");
		Date acceptTime2 = UtilTool.strToDate(o2.getAcceptTime(), "yyyy-MM-dd");
		if(acceptTime1.after(acceptTime2))
			return 1;
		return -1;
	}

}

UtilTool.java代码如下：

package com.compare.util;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class UtilTool {
	
	public static Date strToDate(String str,String formate){
		
		DateFormat df = new SimpleDateFormat(formate);
		Date d = null;
		try{
			d = df.parse(str);
		}catch (Exception e) {
			e.printStackTrace();
		}
		return d;
	}
}

Test.java代码如下：

package com.compare.test;

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

import com.compare.bean.Step;
import com.compare.util.StepComparator;

public class Test {
	
	public static void main(String[] args) {
		testComparator();
	}
	
    public static void testComparator(){
    	List<Step> steps = new ArrayList<Step>();
    	steps.add(new Step("1997-12-03","HONGKONG"));
    	steps.add(new Step("1997-12-04","BEIJING"));
    	steps.add(new Step("1997-11-04","SHANGHAI"));
    	StepComparator comparator = new StepComparator();
    	Collections.sort(steps,comparator);
    	if(steps!=null&&steps.size()>0){
    		for(Step step:steps){
    			System.out.println(step.getAcceptTime());
    			System.out.println(step.getAcceptAddress());
    			System.out.println("==================");
    		}
    	}
    }

}

运行结果如下：

1997-11-04
SHANGHAI
==================
1997-12-03
HONGKONG
==================
1997-12-04
BEIJING
==================