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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>GOF 模式：Structural（续）</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 13 页（共18 页）</nobr></font></td>
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<p>
<b>Bridge</b>
</p>
<p>目标：<br>
			解耦抽象及其实现，这样二者可以独立变化。
			</p>
<p>说明：<br>
			当抽象可以有几个可能的实现时，通常容纳它们的方式是使用继承性，将一个实现永久性地绑定到抽象，从而使得独立地修改、扩展和重用抽象和实现变得很困难。Bridge 模式不是将抽象与实现结合到许多不同的类中，而是将抽象实现为可以动态结合的独立的类。
			</p>
<p>UML 图：<br>
			
<img src="images/SCEA-Bridge.gif" alt="Bridge 的 UML 图">
			</p>
<p>益处：<br>
			
<ul>
<li>解耦接口与实现。</li>
<li>改进扩展性。</li>
<li>对客户机隐藏实现细节。</li>
</ul>
			
</p>
<p>什么时候使用？<br>
			应当在以下情况下使用 Bridge 模式： 
			<ul>
<li>想要避免抽象及其实现之间的永久绑定。 <br>
<br>
</li>
<li>抽象及其实现应当可以用子类扩展。<br>
<br>
</li>
<li>在抽象的实现中的改变应当不会对客户机有影响，就是说，不必重新编译它们的代码。 </li>
</ul>
			
</p>
<p>
<b>Composite</b>
</p>
<p>目标：<br>
			将对象组合为树结构以表示部分-整体层次结构。Composite 模式使客户机统一地处理单独的对象和对象的复合体。
			</p>
<p>说明：<br>
			Composite 模式将对象结合为树结构，以表示整个层次结构，或者表示层次结构的一部分。这种递归组合使客户可以统一地处理单独的对象和对象复合体。
			</p>
<p>UML 图：<br>
			
<img src="images/SCEA-Composite.gif" alt="Composite 的 UML 图">
			</p>
<p>益处：<br>
			
<ul>
<li>定义包含原始对象和组合对象的层次结构。<br>
<br>
</li>
<li>使客户机更简单。 <br>
<br>
</li>
<li>使增加新类型的组件更容易。 </li>
</ul>
			
</p>
<p>什么时候使用？<br>
			可以在以下情况下使用 Composite 模式： 
			<ul>
<li>希望表示对象的部分-整体层次结构的时候。<br>
<br>
</li>
<li>希望客户机可以忽略对象组合与单独的对象之间的不同。 <br>
<br>
</li>
</ul>
			
</p>
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