J2SE5.0新特性示例---循环语句的增强

Dear 丶 2021-11-14 00:04 135阅读 0赞

#### 循环语句的增强 ####

之前类似这样的语句：

<table style="border-right:medium none;border-top:medium none;background:#C0C0C0 0% 50%;border-left:medium none;width:378pt;border-bottom:medium none;border-collapse:collapse;"> 
 <tbody> 
 <tr> 
 <td style="border-right:1pt solid;border-top:1pt solid;border-left:1pt solid;width:378pt;border-bottom:1pt solid;"> void cancelAll(Collection c) { &nbsp;&nbsp;&nbsp; for (Iterator i = c.iterator(); i.hasNext(); ) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; TimerTask tt = (TimerTask) i.next(); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tt.cancel(); &nbsp;&nbsp;&nbsp; } } </td> 
 </tr> 
 </tbody> 
</table>

以后可以这样写：

<table style="border-right:medium none;border-top:medium none;background:#C0C0C0 0% 50%;border-left:medium none;width:378pt;border-bottom:medium none;border-collapse:collapse;"> 
 <tbody> 
 <tr> 
 <td style="border-right:1pt solid;border-top:1pt solid;border-left:1pt solid;width:378pt;border-bottom:1pt solid;"> void cancelAll(Collection c) { &nbsp;&nbsp;&nbsp; for (Object o : c) &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((TimerTask)o).cancel(); } </td> 
 </tr> 
 </tbody> 
</table>

有时候我们可能写出这样的代码：

<table style="border-right:medium none;border-top:medium none;background:#C0C0C0 0% 50%;border-left:medium none;width:378pt;border-bottom:medium none;border-collapse:collapse;"> 
 <tbody> 
 <tr> 
 <td style="border-right:1pt solid;border-top:1pt solid;border-left:1pt solid;width:378pt;border-bottom:1pt solid;"> List suits = ...; List ranks = ...; List sortedDeck = new ArrayList(); for (Iterator i = suits.iterator(); i.hasNext(); ) &nbsp;&nbsp;&nbsp; for (Iterator j = ranks.iterator(); j.hasNext(); ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sortedDeck.add(new Card(i.next(), j.next())); </td> 
 </tr> 
 </tbody> 
</table>

这段代码不会按照我们设想的那么工作，因为每次第二个for语句的执行都会引发i.next()的执行，实际上我们没有达到对i进行遍历的目的，而且可能会引起一个NoSuchElementException异常。

解决的一个办法是改写成如下代码：

<table style="border-right:medium none;border-top:medium none;background:#C0C0C0 0% 50%;border-left:medium none;width:378pt;border-bottom:medium none;border-collapse:collapse;"> 
 <tbody> 
 <tr> 
 <td style="border-right:1pt solid;border-top:1pt solid;border-left:1pt solid;width:378pt;border-bottom:1pt solid;"> for (Iterator i = suits.iterator(); i.hasNext(); ) { &nbsp;&nbsp;&nbsp; Suit suit = (Suit) i.next(); &nbsp;&nbsp;&nbsp; for (Iterator j = ranks.iterator(); j.hasNext(); ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sortedDeck.add(new Card(suit, j.next())); } </td> 
 </tr> 
 </tbody> 
</table>

利用java语言的新特性，我们可以这样写：

<table style="border-right:medium none;border-top:medium none;background:#C0C0C0 0% 50%;border-left:medium none;width:378pt;border-bottom:medium none;border-collapse:collapse;"> 
 <tbody> 
 <tr> 
 <td style="border-right:1pt solid;border-top:1pt solid;border-left:1pt solid;width:378pt;border-bottom:1pt solid;"> for (Suit suit : suits) &nbsp;&nbsp;&nbsp; for (Rank rank : ranks) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sortedDeck.add(new Card(suit, rank)); &nbsp; </td> 
 </tr> 
 </tbody> 
</table>

这段代码是不是很漂亮？

转载于:https://www.cnblogs.com/jackyzhong/archive/2005/05/13/154804.html