首先是一個 關于周遊的小例子:
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());
}
}
至于這兩者的性能:
通過測試發現,第二種方式的性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()的疊代時間
* keySet():疊代後隻能通過get()取key
* entrySet():疊代後可以e.getKey(),e.getValue()取key和value。傳回的是Entry接口
* 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();
//結束世界并且也是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));
}
}