keySet()与entrySet()

keySet()与entrySet()
Java代码
import java.util.Calendar;  
import java.util.Date;  
import java.util.HashMap;  
import java.util.Iterator;  
import java.util.Map.Entry;  
 
/** 
* 测试keySet()与entrySet()的迭代时间 
* keySet():迭代后只能通过get()取key 
* entrySet()：迭代后可以e.getKey()，e.getValue()取key和value。返回的是Entry接口 
* 最后说明下keySet()的速度比entrySet()慢了很多。看来以后要考虑用entrySet()了 
* @author YL 
* @date 2009.6.10 
*/ 
public class HashMapTest      
{  
    public static void main(String[] args)   
    {  
        HashMap<String,String> kmap = new HashMap<String,String>();  
        HashMap<String, String> emap = new HashMap<String, String>();  
          
        //装数据  
        for (int i = 0; i < 1000; i++)   
        {  
            kmap.put(""+i, "YL");  
        }  
        for (int i = 0; i < 1000; i++)   
        {  
            emap.put(""+i, "ZT");  
        }  
          
        long stimes = System.currentTimeMillis();  
        long ctimes = Calendar.getInstance().getTimeInMillis();  
        long dtimes = new Date().getTime();  
          
        //初始时间 这里我用了三种取值方式 最后发现System.currentTimeMillis();是最直接的取值方法  
        System.out.println(stimes+" "+ctimes+"  "+dtimes);  
          
        Iterator<String> ktor = kmap.keySet().iterator();  
        while(ktor.hasNext())  
        {  
            System.out.println(ktor.next());  
        }  
          
        long stimes1 = System.currentTimeMillis();  
        long ctimes1 = Calendar.getInstance().getTimeInMillis();  
        long dtimes1 = new Date().getTime();  
          
        //结束世界并且也是entrySet的开始时间  
        System.out.println((stimes1-stimes)+"   "+(ctimes1-ctimes)+"    "+(dtimes1-dtimes));  
        System.out.println(stimes1+"    "+ctimes1+" "+dtimes1);  
          
        Iterator<Entry<String, String>> itor = emap.entrySet().iterator();  
        while(itor.hasNext())  
        {  
            Entry<String, String> e = itor.next();  
            //System.out.println(e.getKey());  
            System.out.println(e.getValue());  
        }  
          
        long stimes2 = System.currentTimeMillis();  
        long ctimes2 = Calendar.getInstance().getTimeInMillis();  
        long dtimes2 = new Date().getTime();  
        System.out.println(stimes2+"    "+ctimes2+" "+dtimes2);  
        System.out.println((stimes2-stimes1)+"  "+(ctimes2-ctimes1)+"   "+(dtimes2-dtimes1));  
    }  
}