java map 倒序_java compareTo对map中的元素进行倒序排序

类ComparatorList

import java.util.Comparator;

import java.util.Map;

public class ComparatorList implements Comparator{

private String compareStr;

public ComparatorList(){

}

public

ComparatorList(String compareStr){

this.compareStr=compareStr;

}

@Override

public int compare(Object o1, Object o2) {

int flag2=0;

Map map1=(Map)o1;

Map map2=(Map)o2;

System.out.println("map1.get(compareStr):"+map1.get(compareStr));

System.out.println("map2.get(compareStr):"+map2.get(compareStr));

int

flag=String.valueOf(map1.get(compareStr)).compareTo(String.valueOf(map2.get(compareStr)));

//倒序

if(flag>0){

flag2=-1;

}else if(flag<0){

flag2=1;

}

System.out.println(flag2);

return flag2;

}

}

类Test3

package com.mrlun.test;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import edu.emory.mathcs.backport.java.util.Collections;

public class Test3 {

public void test(){

}

public static void main(String[] args) {

Map map3=new HashMap();

map3.put("fruits", "apple");

map3.put("eat_time", "20140721

00:01:29");

Map map1=new HashMap();

map1.put("fruits",

"orange");

map1.put("eat_time", "20140720

00:20:29");

Map map2=new HashMap();

map2.put("fruits", "pear");

map2.put("eat_time", "20140721

00:05:29");

List list=new

ArrayList();

list.add(map1);

list.add(map2);

list.add(map3);

Collections.sort(list,new

ComparatorList("eat_time"));

for(Object o:list ){

Map

m=(Map)o;

System.out.println(m.get("fruits")+"："+m.get("eat_time"));

}

}

}

// output：

pear：20140721 00:05:29

apple：20140721 00:01:29

orange：20140720 00:20:29

总结：

要想实现自己的比较器，就要实现java提供的Comparator接口，并且覆盖其compare方法，返回值有-1、0、1，分别表示比较的结果，默认是升序排列，要想实现倒序，则要加上特殊处理的代码，如上。