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<div align="center" class="title">JAVA程序員必讀：基礎篇(6)---接口和包</div>
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<div align="center"><font color="#666666">編譯：ZSC/太平洋網絡學院</font></div>
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<div align="right" class="gray"><a href="mailto:tntst@pconline.com.cn">［責編:爆破手］</a></div>
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<p class="article"> <b><span class="article">6.1.3 執行接口</span></b></p>
<p class="article"> 為了使用接口，你要編寫執行接口的類。如果一個類可以執行一個接口，那么這個類就提供了執行定義在接口中的所有方法的方法。
</p>
<p class="article"> 一個接口定義了行為的協議。一個類可以根據定義在接口中的協議來執行接口。為了聲明一個類執行一個接口，要包括一條執行語句在類的聲明中。你的類可以執行多個接口（因為JAVA平臺支持接口的多個繼承），因此可以在implements后面列出由類執行的接口系列，這些接口是以逗號分隔的。</p>
<p class="article"> 以下是一個applet的部分例子，它執行StockWatcher接口： </p>
<p class="article">public class StockApplet extends Applet implements
StockWatcher {</p>
<p class="article"> ...</p>
<p></p>
<p class="article"> public void valueChanged(String tickerSymbol,
double newValue) {</p>
<p class="article"> if (tickerSymbol.equals(sunTicker)) {</p>
<p class="article"> ...</p>
<p class="article"> } else if (tickerSymbol.equals(oracleTicker))
{</p>
<p class="article"> ...</p>
<p class="article"> } else if (tickerSymbol.equals(ciscoTicker)) {</p>
<p class="article"> ...</p>
<p class="article"> }</p>
<p class="article"> }</p>
<p class="article">}</p>
<p class="article"> 這里注意，這個類引用了定義在StockWatcher.sunTicker的常量，如oracleTicker等等。執行接口的類繼承了定義在接口中的常量。因此這些類可以使用簡單的名字來引用常量。你可以象下面的語句，使其它任何類使用接口常量：
</p>
<p class="article">StockWatcher.sunTicker</p>
<p class="article"> 從本質上講，當類執行一個接口的時候，就簽定了一個契約。所有的類必須執行所有定義在接口以及它的superinterfaces中的方法，以及類必須定義為abstract。這個方法的簽名（名字和在類中參數類型的數目）必須匹配方法的簽名。StockApplet執行SockWatcher接口，因此applet提供了valueChanged方法。這個方法公開地更新了applets的顯示或者使用這個信息。</p>
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