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<div align="center" class="title">JAVA程序員必讀：基礎篇(5)---類和繼承</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> <span class="article"><b>5.1.7.3 初始化塊實例變量</b></span></p>
<p class="article"> 有時候，類包含了許多構造函數，并且每個構造函數允許調用者為新對象的不同實例變量提供不同的初始數值。比如，java.awt.Rectangle就有三個構造函數：
</p>
<p class="article">Rectangle();</p>
<p class="article">Rectangle(int width, int height);</p>
<p class="article">Rectangle(int x, int y, int width, int height);</p>
<p class="article"> 沒有參數的構造函數沒有讓調用者提供初始數值，而另外的兩個構造函數讓用戶設置初始數值（大小與原點）。然而，所有的實例變量都必須初始化。在本例子中，構造函數完成了這些初始化工作。比如以上的這三個構造函數是這樣初始化的：
</p>
<p class="article">Rectangle() {</p>
<p class="article"> this(0,0,0,0);</p>
<p class="article">}</p>
<p class="article">Rectangle(int width, int height) {</p>
<p class="article"> this(0,0,width,height);</p>
<p class="article">}</p>
<p class="article">Rectangle(int x, int y, int width, int height)
{</p>
<p class="article"> this.x = x;</p>
<p class="article"> this.y = y;</p>
<p class="article"> this.width = width;</p>
<p class="article"> this.height = height;</p>
<p class="article">}</p>
<p class="article"> Java語言支持實例初始化塊，但是它不能用在無記錄類（不能聲明構造函數）中。使用構造函數比較好的原因有：
</p>
<ol>
<p>
<li class="article">所有的初始化代碼放置在一起，這樣使得代碼更容易維護和閱讀。</li>
<p></p>
<p>
<li class="article">缺省值可以顯性地處理。</li>
<p></p>
</ol>
<p class="article"> 程序員廣泛使用構造函數，即使JAVA的新手也是一樣。而實例初始化程序可能導致有些程序員對代碼的閱讀感到困難。</p>
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