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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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<p><b> <span class="article">5.1.7 理解實例和類成員</span></b></p>
<p></p>
<p class="article"> 為了指定成員變量是一個類變量，你可以使用static關鍵字。比如，讓我們來修改以下AnIntegerNamedX類讓x變量成為一個類變量：</p>
<p class="article">class AnIntegerNamedX {</p>
<p class="article"> static int x;</p>
<p class="article"> public int x() {</p>
<p class="article"> return x;</p>
<p class="article"> }</p>
<p class="article"> public void setX(int newX) {</p>
<p class="article"> x = newX;</p>
<p class="article"> }</p>
<p class="article">}</p>
<p class="article"> 結果輸出為：</p>
<p class="article">myX.x = 2</p>
<p class="article">anotherX.x = 2</p>
<p class="article"> 結果輸出相同是因為x現在是一個類變量了，因此就只有一個變量的副本了，它被AnIntegerNamedX的所有實例所共享，包括myX和anotherX。當你在任一個實例中調用setX的時候，你就改變了AnIntergerNamedX所有實例的數值。
</p>
<p class="article"> 當定義一個方法的時候，你可以指定方法為類方法而不是實例方法。類方法只能操作類變量而不能訪問定義在類中的實例變量。
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