首先是一個 關於遍歷的小例子：

public static void main(String[] args) {
        // TODO Auto-generated method stub
        Map<String, String> maps = new HashMap<String, String>();
        maps.put("111", "111a");
        maps.put("222", "222b");
        maps.put("333", "333c");
        maps.put("444", "444d");
        maps.put("555", "555e");
        maps.put("666", "666f");
        
        for(String str : maps.keySet()){
            System.out.println(str + ":" + maps.get(str));
        }
        
        System.out.println("--------------");
        
        for(Entry<String, String> str : maps.entrySet()){
            System.out.println(str + "   " + str.getKey() + ":" + str.getValue());
        }

    }
 

至於這兩者的效能：

通過測試發現,第二種方式的效能通常要比第一種方式高一倍。

例子如下：

import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;

/**
 * 測試keySet()與entrySet()的迭代時間
 * keySet():迭代後只能通過get()取key
 * entrySet()：迭代後可以e.getKey()，e.getValue()取key和value。返回的是Entry介面
 * 最後說明下keySet()的速度比entrySet()慢了很多。看來以後要考慮用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>();
		
		//裝資料
		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();
		
		//初始時間 這裡我用了三種取值方式 最後發現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();
		
		//結束世界並且也是entrySet的開始時間
		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));
	}
}