java hashmap遍历顺序_HashMap的遍历和排序

1.HashMap的遍历

package com.sheepmu;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

public class KMPText

{

public static void main(String[] args)

{

Map map=new HashMap();

map.put("key1", "bb");

map.put("key0", "aaa");

map.put("key3", "dddd");

map.put("key2", "cccccccc");

//遍历方法0 我个人最喜欢的遍历。集合的遍历还是用for-each的遍历是最爽滴~

for(Map.Entry entry:map.entrySet())//值和value都需要遍历时

{

String key= entry.getKey().toString();

String value=entry.getValue().toString();

System.out.println("entry--->"+entry);

// System.out.println("key---->"+key+" value---->"+value+" ");

}

//遍历方法1 此方法效率也很高

Iterator it=map.entrySet().iterator();

while(it.hasNext())

{

Map.Entry entry=(Map.Entry) it.next();

String key= entry.getKey().toString();

String value=entry.getValue().toString();

System.out.println("key---->"+key+" value---->"+value+" ");

}

}

}

2.HashMap的排序

(1).方法：把map的entry取出来放到list里面，这样就相当于排list

eg:对上面例子的HashMap按key从小到大排orvalue从长到短排

package com.sheepmu;

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Map.Entry;

public class KMPText

{

public static void main(String[] args)

{

Map map=new HashMap();

map.put("key1", "bb");

map.put("key0", "aaa");

map.put("key3", "dddd");

map.put("key2", "cccccccc");

//遍历 hashmap

for(Map.Entry entry:map.entrySet())

{

String key= entry.getKey().toString();

String value=entry.getValue().toString();

System.out.println("key---->"+key+" value---->"+value+" ");

}

//按要求排序hashmap

List> list=new ArrayList>(map.entrySet());//!!!

Collections.sort(list, new Comparator>(){//按key值字符串比较从小到大

@Override

public int compare(Entry o1,Entry o2) {

return o1.getKey().compareTo(o2.getKey());

}});

System.out.println("list---->"+list);

Collections.sort(list, new Comparator>(){//按value值字符串长度比较从大到小

@Override

public int compare(Entry o1,Entry o2) {

return o2.getValue().length()-o1.getValue().length();

}});

System.out.println("list---->"+list);

}

}

注：如果希望遍历后的顺序与put进去的顺序一致，则采用LinkendHashMap

package com.sheepmu;

import java.util.HashMap;

import java.util.LinkedHashMap;

import java.util.Map;

public class KMPText

{

public static void main(String[] args)

{

Map map=new HashMap();

map.put("key1", "bb");

map.put("key0", "aaa");

map.put("key3", "dddd");

map.put("key2", "cccccccc");

System.out.println("hashmap--->"+map);

Map lmap=new LinkedHashMap();

lmap.put("key1", "bb");

lmap.put("key0", "aaa");

lmap.put("key3", "dddd");

lmap.put("key2", "cccccccc");

System.out.println("linkedhashmap--->"+lmap);

}

}

原文：http://blog.youkuaiyun.com/sheepmu/article/details/25751527