keySet()与entrySet()

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));
	}
}

评论

4 楼 durong11 2013-10-11  

不错~ 值得学习

3 楼 Evilover3 2013-05-07  

谢谢分享，学习了

2 楼 BuN_Ny 2013-01-11  

Y???????????

1 楼 ruijie19871128 2010-09-26  

总结的不错。。以后我也只有entitySet了。