要遍历一个Hashtable，api中提供了如下几个方法可供我们遍历：
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keys() - returns an Enumeration of the keys of this Hashtable keySet() - returns a Set of the keys entrySet() - returns a Set of the mappings elements() - returns an Enumeration of the values of this Hashtable |
4种方法，那种更好呢，写段代码来比较一下吧：
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import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map.Entry;
public class HashtableTest
{ public static void main(String[]
args) { long start
= 0; long end
= 0; Hashtable<String, String> table = new Hashtable<String,
String>(); for( int i
= 0; i < 1000000; i++) { table.put( "key:" +
i, "value:" + i); }
//1、使用keys()
start = System. currentTimeMillis();
Enumeration<String> en1 = table.keys();
while(en1.hasMoreElements())
{ en1.nextElement();
}
end = System. currentTimeMillis();
System. out.println( "Enumeration
keys costs " + (end - start) + " milliseconds" ); //2、使用elements()
start = System. currentTimeMillis();
Enumeration<String> en2 = table.elements();
while(en2.hasMoreElements())
{ en2.nextElement();
}
end = System. currentTimeMillis();
System. out.println( "Enumeration
elements costs " + (end - start) + " milliseconds" ); //3、使用keySet()
start = System. currentTimeMillis();
Iterator<String> it1 = table.keySet().iterator();
while(it1.hasNext())
{ it1.next();
}
end = System. currentTimeMillis();
System. out.println( "Iterator
keySet costs " + (end - start) + " milliseconds" ); //4、使用entrySet()
start = System. currentTimeMillis();
Iterator<Entry<String, String>> it2 = table.entrySet().iterator();
while(it2.hasNext())
{ it2.next();
}
end = System. currentTimeMillis();
System. out.println( "Iterator
entrySet costs " + (end - start) + " milliseconds" ); }
}
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运行结果如下：
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Enumeration keys costs 16 milliseconds
Enumeration elements costs 15 milliseconds
Iterator keySet costs 17 milliseconds
Iterator entrySet costs 16 milliseconds
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通过运行结果显示，在如今jdk的版本下，两者差距不是很大，不过使用Enumeration去遍历会稍微快一些。