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11.3 概述</div>
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<p class="Element10">
类是一种数据类型，它包含了数据以及对数据进行操作的子程序（函数和任务）。类的数据被称为类属性，它的子程序被称为方法，无论是类属性还是方法都是类的成员。类属性和方法结合在一起，定义了某种类型的对象的内容和能力。 </p>
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例如，一个数据包可以是一个对象。它可能具有一个命令域、一个地址、一个序列号、一个时戳、以及一个数据包净荷。另外，一个数据包可以实现多项不同的任务：初始化数据包、设置命令、读取数据包的状态、或者检查序列号。尽管每一个数据包都是不同的，然而作为一个类，数据包具有某些固有的属性，这些固有属性可以在类的定义中进行说明。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00340"><pre class="Element12"><span style="color: #0000FF">class</span> Packet<span style="color: #800080">;</span>
<span style="color: #008000">// 数据或类属性</span>
<span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">3</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> command<span style="color: #800080">;</span>
<span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">40</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> address<span style="color: #800080">;</span>
<span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">4</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> master_id<span style="color: #800080">;</span>
<span style="color: #0000FF">integer</span> time_requested<span style="color: #800080">;</span>
<span style="color: #0000FF">integer</span> time_issued<span style="color: #800080">;</span>
<span style="color: #0000FF">integer</span> status<span style="color: #800080">;</span>
<span style="color: #008000">// 初始化</span>
<span style="color: #0000FF">function</span> <span style="color: #0000FF">new</span><span style="color: #800080">();</span>
command <span style="color: #800080">=</span> IDLE<span style="color: #800080">;</span>
address <span style="color: #800080">=</span> <span style="color: #FF0000">41</span><span style="color: #800080">'</span><span style="color: #0000FF">b</span><span style="color: #FF0000">0</span><span style="color: #800080">;</span>
master_id <span style="color: #800080">=</span> <span style="color: #FF0000">5</span><span style="color: #800080">'</span><span style="color: #0000FF">b</span><span style="color: #FF0000">x</span><span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span>
<span style="color: #008000">// 方法</span>
<span style="color: #008000">// 公共访问入口点</span>
<span style="color: #0000FF">task</span> clean<span style="color: #800080">();</span>
command <span style="color: #800080">= </span><span style="color: #FF0000">0</span><span style="color: #800080">;</span>
address <span style="color: #800080">= </span><span style="color: #FF0000">0</span><span style="color: #800080">;</span>
master_id <span style="color: #800080">=</span> <span style="color: #FF0000">5</span><span style="color: #800080">'</span><span style="color: #0000FF">b</span><span style="color: #FF0000">x</span><span style="color: #800080">;</span>
<span style="color: #0000FF">endtask</span>
<span style="color: #0000FF">task</span> issue_request<span style="color: #800080">(</span><span style="color: #0000FF">int</span> delay<span style="color: #800080">);</span>
<span style="color: #008000">// 向总线发送请求</span>
<span style="color: #0000FF">endtask</span>
<span style="color: #0000FF">function integer</span> current_status<span style="color: #800080">();</span>
current_status <span style="color: #800080">=</span> status<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span>
<span style="color: #0000FF">endclass</span></pre></div></div>
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一个通常的惯例是以大写字母形式书写类名字的第一个字母，这样我们能够很容易地识别类声明。</p></div>
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