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<div align="center" class="title">JAVA程序員必讀：基礎(chǔ)篇(6)---接口和包</div>
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<div align="center"><font color="#666666">編譯：ZSC/太平洋網(wǎng)絡(luò)學(xué)院</font></div>
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<p><b><span class="article">6.1.5 接口不能發(fā)展</span></b></p>
<p class="article"> 如果你將接口傳給其它的程序員，接口有個(gè)限制你應(yīng)該注意：接口不能發(fā)展。下面對此進(jìn)行解釋：</p>
<p class="article"> 假如你想怎樣一個(gè)函數(shù)到StockWatcher。比如，你想增加一個(gè)匯報(bào)當(dāng)前股票價(jià)格的方法，而不管數(shù)值是否被改變了：
</p>
<p class="article">public interface StockWatcher {</p>
<p class="article"> final String sunTicker = "SUNW";</p>
<p class="article"> final String oracleTicker = "ORCL";</p>
<p class="article"> final String ciscoTicker = "CSCO";</p>
<p class="article"> void valueChanged(String tickerSymbol, double
newValue); </p>
<p class="article"> void currentValue(String tickerSymbol, double
newValue); </p>
<p class="article">}</p>
<p class="article"> 但是，如果你做了這個(gè)改變的話，執(zhí)行老版本的StockWatcher接口的所有類都將中斷，因?yàn)樗鼈儾荒軋?zhí)行這個(gè)接口了。接口不能發(fā)展，這是所有程序員要知道的。為了達(dá)到以上增加一個(gè)方法的目的你可以創(chuàng)建更多的界面。比如，你可以創(chuàng)建一個(gè)</p>
<p class="article">StockWatcher的subinterface（子接口）StockTracker：: </p>
<p class="article">public interface StockTracker extends StockWatcher
{</p>
<p class="article"> void currentValue(String tickerSymbol, double
newValue);</p>
<p class="article">}</p>
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