📄 defaultadapter.htm
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<h3><a href="http://caterpillar.onlyfun.net/GossipCN/index.html">From
Gossip@caterpillar</a></h3>
<h1><a href="CppGossip.html">Design Pattern: Default Adapter 模式</a></h1>
在Java中如果要定义事件处理的方式，必须实作EventListener的子介面，例如实作 WindowListener来定义一些视窗事件的处理方式，WindowListener中定义了七个方法：<br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">public interface WindowListener extends EventListener {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowOpened(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosing(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosed(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowIconified(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDeiconified(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowActivated(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDecativated(WindowEvent e);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
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可以定义一个类别来实作这个介面，以完全想要的事件处理，例如：<br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">public class WindowEventHandler implements WindowListener {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowOpened(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosing(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosed(WindowEvent e) {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> System.exit(0);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowIconified(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDeiconified(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowActivated(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDecativated(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
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然而这有个缺点，实作介面的原则是您必须实作当中所定义的所有方法，即使您对某些事件并不感兴趣，您也必须实作一个没有内容的空方法，代表您已经实作了介
面中定义的方法，然而有时，您并不知道介面中到底定义了几个方法，或是知道也不知道方法的确切名称与参数，即使您查了API，在程式中写下一堆没有实作内
容的方法也是很烦人的一件事。<br>
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WindowAdapter类别预先实作了WindowListener介面，每个方法中都是空的实作，如下所示：<br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">public abstract class WindowAdapter </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">
implements WindowListener {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowOpened(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosing(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosed(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowIconified(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDeiconified(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowActivated(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowDecativated(WindowEvent e) {}</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
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可以继承WindowAdapter类别，并重新定义一些您所感兴趣的事件，如此一来，就可以避开之前所提及的，直接实作 WindowListener介面的缺点，如下所示：<br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">public class WindowEventHandler extends WindowAdapter {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> public void windowClosed(WindowEvent e) {</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> System.exit(0);</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
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这就是Default Adapter模式，它使用一个中介的Adapter类别来将真正感兴趣的事件实作类别，配接至事件处理介面，上面的程式其 UML 图如下：<br>
<div style="text-align: center;"><img style="width: 159px; height: 211px;" alt="DefaultAdapter" title="DefaultAdapter" src="images/defaultAdapter-1.jpg"><br>
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将上图一般化，Default Adapter模式的结构如下所示：<br>
<div style="text-align: center;"><img style="width: 127px; height: 143px;" alt="DefaultAdapter" title="DefaultAdapter" src="images/defaultAdapter-2.jpg"><br>
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