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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>示例问题</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 9 页（共9 页）</nobr></font></td>
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<font size="2" face="Verdana, Arial, Helvetica"><b>问题 1：</b>
<p> 如果相关的会话没有名为 <code>str</code> 的属性，访问下面 JSP 页面的结果将是什么？</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
&lt;%!
    String str;
    public void jspInit()
    {
     str = (String)session.getAttribute("str");
    }
%&gt;
</code>
</pre>
<p>字符串是：<code>&lt;%= str %&gt;</code>。</p>
<p>
<b>选择：</b>
</p>
<ul>
<li>
<b>A.</b> 输出&ldquo;null&rdquo;</li>
<li>
<b>B.</b>抛出 <code>NullPointerException</code>
</li>
<li>
<b>C.</b> 代码没有编译</li>
<li>
<b>D.</b> 以上都不是</li>
</ul>
<p>
<b>正确答案：</b>
</p>
<ul>
<li>
<b>C</b>
</li>
</ul>
<p>
<b>说明：</b>
</p>
<p>JSP 引挚在 <code>_jspService()</code> 方法中声明和初始化 9 个对象。这些隐式对象变量是 <code>application</code>、<code>session</code>、<code>request</code>、<code>response</code>、<code>out</code>、<code>page</code>、<code>pageContext</code>、<code>config</code> 和 <code>exception</code>。因为它们是以局部方式声明到 <code>_jspService()</code> 方法，所以它们不可以在 <code>jspInit()</code> 方法中访问，这表明这些代码将不编译。如果该代码是在 <code>jspService()</code> 方法中，它会无错误地编译，并输出&ldquo;null&rdquo;。因此，选项 A、B 和 D 是不正确的，选项 C 是正确的。</p>
<p>
<b>问题 2：</b>
</p>
<p>尝试访问该 JSP 页面的结果将是什么？</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
&lt;% x=10;% &gt;
&lt;% int x=5;% &gt;
&lt;%! int x; %&gt;
x= &lt;%=x%&gt;
x= &lt;%=this.x%&gt;
</code>
</pre>
<p>字符串是 <code>&lt;%= str %&gt;</code>。</p>
<p>
<b>选择：</b>
</p>
<ul>
<li>
<b>A.</b> 代码没有编译，因为在声明前使用了 x。</li>
<li>
<b>B.</b> 输出 x=5 ，x=10</li>
<li>
<b>C.</b> 输出 x=10 ，x=5</li>
<li>
<b>D.</b> 输出 x=10 ，x=0</li>
<li>
<b>E.</b> 以上都不是</li>
</ul>
<p>
<b>正确答案：</b>
</p>
<ul>
<li>
<b>B</b>
</li>
</ul>
<p>
<b>说明：</b>
</p>
<p>该声明将创建一个实例变量 x，并把它初始化为 0。然后在 <code>service()</code> 方法中，把它修改为 10。然后声明一个称为 x 的局部变量，并给予值 5。当输出 x，它输出了值 5的局部版本。当谈到 <code>this.x</code>，引用的是实例变量 x，它输出 10。因此选项 A、C 和 D 是不正确的，选项 B 是正确的。</p>
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