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<String,String> map=new HashMap<String,String>();
		 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<String, String> 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<String,String> map=new HashMap<String,String>();
		 map.put("key1", "bb");
		 map.put("key0", "aaa");
		 map.put("key3", "dddd");
		 map.put("key2", "cccccccc");

		 //遍历 hashmap
		 for(Map.Entry<String, String> 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<Map.Entry<String, String>> list=new ArrayList<Map.Entry<String, String>>(map.entrySet());//!!!
		  Collections.sort(list, new Comparator<Map.Entry<String, String>>(){//按key值字符串比较从小到大
			@Override
			public int compare(Entry<String, String> o1,Entry<String, String> o2) {
				return o1.getKey().compareTo(o2.getKey());
			}});

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

		  Collections.sort(list, new Comparator<Map.Entry<String, String>>(){//按value值字符串长度比较从大到小
				@Override
				public int compare(Entry<String, String> o1,Entry<String, String> 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<String,String> map=new HashMap<String,String>();
		 map.put("key1", "bb");
		 map.put("key0", "aaa");
		 map.put("key3", "dddd");
		 map.put("key2", "cccccccc");
		 System.out.println("hashmap--->"+map); 

		 Map<String,String> lmap=new LinkedHashMap<String,String>();
		 lmap.put("key1", "bb");
		 lmap.put("key0", "aaa");
		 lmap.put("key3", "dddd");
		 lmap.put("key2", "cccccccc");
		 System.out.println("linkedhashmap--->"+lmap); 

	}

}