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<div align="center" class="title">JAVA程序員必讀：基礎篇（2）面向對象編程概念</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><b><span class="article">2.7.3ClickMe Applet中的類</span></b></p>
<p class="article"> 因為代表在屏幕上點的對象是很簡單，接下來讓我們看看這個名為spot的類吧。它聲明了三個實例變量：包括點半徑的size，包含點當前水平位置的x坐標以及包含點當前垂直位置的y坐標：</p>
<p class="article"><span class="blue">public class Spot {</span></p>
<p class="article"><span class="blue"> //實例變量</span></p>
<p class="article"><span class="blue"> public int size;</span></p>
<p class="article"><span class="blue"> public int x, y;</span></p>
<p></p>
<p class="article"><span class="blue"> //構造函數</span></p>
<p class="article"><span class="blue"> public Spot(int intSize) {</span></p>
<p class="article"><span class="blue"> size = intSize;</span></p>
<p class="article"><span class="blue"> x = -1;</span></p>
<p class="article"><span class="blue"> y = -1;</span></p>
<p class="article"><span class="blue"> }</span></p>
<p class="article"><span class="blue">}</span></p>
<p class="article"> 另外，類有一個構造函數，它用來初始化由類創建的新對象。構造函數跟類有相同的名字。這個構造函數初始化所有三個對象的變量。Size的初始化數值是在調用的時候座位參數提供的。x和y變量都被設置為-1，這里-1的目的是為了讓點在開始的時候處于屏幕的外面，即產生假不可視的效果。</p>
<p class="article"> 這個applet是在applet初始化的時候創建了一個新的點對象。下面是applet類的相關代碼：
</p>
<p class="article"><span class="blue">private Spot spot = null;</span></p>
<p class="article"><span class="blue">private static final int RADIUS
= 7;</span></p>
<p class="article"><span class="blue">...</span></p>
<p class="article"><span class="blue">spot = new Spot(RADIUS);</span></p>
<p class="article">第一行聲明了一個名為spot的變量，它是Spot數據類型，并且初始化這個變量為NULL。第二行聲明了一個整型變量，名為RADIUS，它的值為7。最后一行是創建一個對象。New關鍵字為對象分配了內存空間。Spot(RADIUS)調用了上面已經描述了的構造函數并且傳遞RADIUS數值，這樣點對象的size就被設置為7。如圖12所示的左圖代表了Spot類，而右邊的是代表了spot對象。</p>
<p></p>
<p class="article"><img src="../images/10717/Image50.gif" width=418 height=139></p>
<p class="article">（圖12）</p>
<p class="article"></p>
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