HashMap的遍历和排序

Posted 2020-08-10 ldxsuanfa

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都须要遍历时
		 {
			 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                       此方法效率也非常高
		 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:对上面样例的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值字符串比較从小到大
			@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值字符串长度比較从大到小
				@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：假设希望遍历后的顺序与put进去的顺序一致，则採用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); 
		 		 
	}
	
}