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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><b><span class="article">（3）存取器函数</span></b></p>
<p class="article"> 首先讲解一下获得String或者StringBuffer的长度：</p>
<p class="article"> 获得有关对象信息的方法称为存取器函数。你可以用在字符串和字符串缓冲区的一个存取器方法是length方法，它可以包含在字符串或者字符串缓冲区的字符的个数。下面给出一个例程，当这个程序执行后，len就将等于17：
</p>
<p class="article">String palindrome = "Dot saw I was Tod";</p>
<p class="article">int len = palindrome.length();</p>
<p class="article"> 除了length，StringBuffer类还有一个方法叫做capacity，它是返回为字符串缓冲区分配的空间大小而不是空间使用了多少。比如，字符串缓冲区的容量在StringsDemo例程中被dest引用时，它是不能改变的，虽然它的长度在每次的循环中增加1。如图15，给出了在dest里面已经有9个字符之后的容量和长度。</p>
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<p class="article">（图15）</p>
<p class="article"> 一个字符串缓冲区的长度是它包含的字符的个数。一个字符串缓冲区的容量是被分配的字符空间的数量。而String类没有capacity方法，因为字符串不能改变。</p>
<p class="article"> 下面讲讲索引String或者String Buffer得到字符：</p>
<p class="article"> 你可以通过使用charAt存取器来在一个特定的位置索引一个字符串或者字符串缓冲区以得到字符串。第一个字符的索引是0，最后一个字符的索引是length()-1。比如，下面的代码在字符串中得到索引为9的字符：
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<p class="article">String anotherPalindrome = "Niagara. O roar again!";
</p>
<p class="article">char aChar = anotherPalindrome.charAt(9);</p>
<p class="article">因为索引是从0开始的，所以索引为9的字符为'O'，如图16所示：</p>
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<p class="article"><img src="/pcedu/empolder/gj/java/images/10717/Image54.gif" width=566 height=120></p>
<p class="article">（图16）</p>
<p class="article"> 使用charAt方法来在特定的索引下得到字符。如图16所示给处了计算字符串最后一个字符的索引的方法，你必须将length方法返回的数值减去1才得到最后一个字符的索引。</p>
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