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<div align="center" class="title">JAVA程序員必讀：基礎(chǔ)篇（2）面向?qū)ο缶幊谈拍?lt;/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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<div align="right" class="gray"><a href="mailto:tntst@pconline.com.cn">［責(zé)編:爆破手］</a></div>
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<p><b><span class="article">2.4實(shí)例和類成員</span></b></p>
<b><span class="article">2.4.5 對(duì)象和類</span></b>
<p class="article"> 你可能會(huì)注意到對(duì)象和類看起來很相似。在現(xiàn)實(shí)世界中，類和對(duì)象之間的區(qū)別經(jīng)常是讓程序員困惑的源泉。在現(xiàn)實(shí)世界中，很明顯，類不能是它們描述的對(duì)象本身。然而，在軟件中很困難來區(qū)分類和對(duì)象。有部分原因是軟件對(duì)象只是現(xiàn)實(shí)世界中的電子模型或者是抽象概念。但是也因?yàn)閷?duì)象通常有時(shí)是指類和實(shí)例。</p>
<p></p>
<p class="article"><b>2.5什么是繼承</b></p>
<p class="article"> 一個(gè)類可以從它的父類繼承狀態(tài)和行為。繼承為組織和構(gòu)造軟件程序提供了一個(gè)強(qiáng)大的和自然的機(jī)理。</p>
<p class="article"> 總得說來，對(duì)象是以類得形式來定義得。你可能現(xiàn)在已經(jīng)可以從它類知道許多對(duì)象了。即使你如知道，如果我告訴你它是一輛自行車，你就會(huì)知道它有兩個(gè)輪子和腳踏板等等。面向?qū)ο笙到y(tǒng)就更深入一些了，它允許類在其它類中定義。比如，山地自行車、賽車以及串座雙人自行車都是各種各樣的自行車。在面向?qū)ο蠹夹g(shù)中，山地自行車、賽車以及串座雙人自行車都是自行車類的子類。同樣地，自行車類是山地自行車、賽車以及串座雙人自行車的父類。這個(gè)父子關(guān)系可以如圖9所示：</p>
<p></p>
<p class="article"><img src="../images/10717/Image47.gif" width=365 height=281></p>
<p class="article">（圖9）</p>
<p class="article"> 每一個(gè)子例從父類中繼承了狀態(tài)。山地自行車、賽車以及串座雙人自行車共享了這些狀態(tài)：速度等。同樣，每一個(gè)子類繼承類從父類的方法，山地自行車、賽車以及串座雙人自行車共享了這些行為：剎車、改變腳踏速度等等。</p>
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