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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中如果要定義事件處理的方式，必須實作EventListener的子介面，例如實作 WindowListener來定義一些視窗事件的處理方式，WindowListener中定義了七個方法：<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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可以定義一個類別來實作這個介面，以完全想要的事件處理，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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然而這有個缺點，實作介面的原則是您必須實作當(dāng)中所定義的所有方法，即使您對某些事件并不感興趣，您也必須實作一個沒有內(nèi)容的空方法，代表您已經(jīng)實作了介
面中定義的方法，然而有時，您并不知道介面中到底定義了幾個方法，或是知道也不知道方法的確切名稱與參數(shù)，即使您查了API，在程式中寫下一堆沒有實作內(nèi)
容的方法也是很煩人的一件事。<br>
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WindowAdapter類別預(yù)先實作了WindowListener介面，每個方法中都是空的實作，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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可以繼承WindowAdapter類別，并重新定義一些您所感興趣的事件，如此一來，就可以避開之前所提及的，直接實作 WindowListener介面的缺點，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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這就是Default Adapter模式，它使用一個中介的Adapter類別來將真正感興趣的事件實作類別，配接至事件處理介面，上面的程式其 UML 圖如下：<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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將上圖一般化，Default Adapter模式的結(jié)構(gòu)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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