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<div align="center" class="title">JAVA程序员必读：基础篇（4）对象和简单数据对象</div>
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<div align="center"><font color="#666666">编译：ZSC/太平洋网络学院</font></div>
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<div align="right" class="gray"><a href="mailto:tntst@pconline.com.cn">［责编:爆破手］</a></div>
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<p class="article"><b>对象和简单数据对象</b></p>
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<p></p>
<p class="article"><b>4.4.2 对象的数组</b></p>
<p class="article"> 数组可以保留引用类型。你可以用创建原始类型数组的方法来创建这样一个数组。以下是一个小的程序ArrayOfStringsDemo,它创建了一个数组包含了三个String对象并且将这三个字符串以小写字母的形式打印出来：
</p>
<p class="article">public class ArrayOfStringsDemo {</p>
<p class="article"> public static void main(String[] args) {</p>
<p class="article"> String[] anArray = { "String One", "String Two",
"String Three" };</p>
<p class="article"> for (int i = 0; i < anArray.length; i++) {</p>
<p class="article"> System.out.println(anArray[i].toLowerCase());</p>
<p class="article"> }</p>
<p class="article"> }</p>
<p class="article">}</p>
<p class="article"> 这个程序中用单一的语句创建和操作了数组。但是，你可以创建一个数组而不用在里面放置任何元素。这对于JAVA新手将是一个容易出错的地方。假如有以下的代码：
</p>
<p class="article">String[] anArray = new String[5];</p>
<p class="article"> 一旦这条语句被执行了，数组anArray就存在了并且有充足的空间来容纳5个String对象。但是，数组并不包含任何的字符串，它是空的。程序必须显性地创建字符串并将他们放置到数组中。这本来示很显然的事情，但是许多JAVA的新手会以为上面的语句已经创建了数组并创建了5和个空的字符串在里面了。这样他们会象如下进行编写代码，结果只会导致一个NullPointerException的异常错误：
</p>
<p class="article">String[] anArray = new String[5];</p>
<p class="article">for (int i = 0; i < anArray.length; i++) {</p>
<p class="article"> // 错误：下面的行将导致一个运行错误</p>
<p class="article"> System.out.println(anArray[i].toLowerCase());</p>
<p class="article">}</p>
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