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《Big C++ 》Third Edition电子书和代码全集-Part1

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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<h3><b>Retrieve Messages</b> use case</h3>

<p>First few steps same as preceding.

<ol>
	<li>User types passcode
		<ul>
			<li><tt>Telephone</tt> notifies <tt>Connection</tt></li>
		</ul>
	</li>
	<li><tt>Connection</tt> asks <tt>Mailbox</tt> to check passcode
		<ul>
			<li>Add "manage passcode" responsibility to <tt>Mailbox</tt></li>
		</ul>
	</li>
	<li>If passcode valid:
		<ul>
			<li><tt>Connection</tt> sets the <tt>Mailbox</tt> as current</li>
			<li>asks <tt>Telephone</tt> to speak mailbox menu</li>
		</ul>
	</li>
</ol>

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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<h3><b>Retrieve Messages</b> use case (cont.)</h3>

<ol start="4">
	<li>User chooses "retrieve msgs" option
		<ul>
			<li><tt>Telephone</tt> passes it on to <tt>Connection</tt></li>
		</ul>
	</li>
	<li><tt>Connection</tt> asks <tt>Telephone</tt> to speak msg menu</li>
	<li>User types in the "listen to current message" option
		<ul>
			<li><tt>Telephone</tt> passes it on to the <tt>Connection</tt></li>
		</ul>
	</li>
	<li><tt>Connection</tt> gets first <tt>Message</tt> from current
		<tt>Mailbox</tt>
		<ul>
			<li>sends its contents to the <tt>Telephone</tt></li>
			<li>Add "retrieve messages" responsibility to Mailbox)</li>
		</ul>
	</li>
</ol>

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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<h3><b>Retrieve Messages</b> use case (cont.)</h3>

<ol start="8">
	<li><tt>Connection</tt> asks the <tt>Telephone</tt> to speak the message
		menu</li>
	<li>User types in "save current message" option</li>
		<ul>
			<li>The <tt>Telephone</tt> passes it on to the <tt>Connection</tt></li>
		</ul>
	</li>
	<li><tt>Connection</tt> tells the <tt>Mailbox</tt> to save current msg
		<ul>
			<li>Modify the responsibilities of <tt>Mailbox</tt> to retrieve, save,
				delete messages)</li>
		</ul>
	</li>
	<li>The <tt>Connection</tt> asks the <tt>Telephone</tt> to speak the
		message menu</li>
</ol>

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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<table>
	<tr>
		<td valign="top">
			<ul>
				<li>The updated <tt>Mailbox</tt> CRC:</li>
				<li>Remaining use cases do not add new information, hence, omitted</li>
			</ul>
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<hr><h2><font color="#009999">25.6.2 CRC Cards for the Voice Mail System (cont.)
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<ul>
	<li>High level reasoning is difficult</li>
	<li>Easily-implemented operations vs. those that appear easy</li>
	<li><strong>Practice</strong></li>
	<li>Many false starts and detours</li>
	<li>Redesign until system works</li>
	<li>CRC cards are meant to fail <i>early</i>, <i>often</i>, and
		<i>inexpensively</i></li>
	<li>Plan to trash your first design</li>
	<li><strong>Practice</strong></li>
</ul>

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<hr><h2><font color="#009999">25.6.3 UML Class Diagrams for the Voice Mail
	System</font></h2>
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<ul>
	<li>Collaboration parts of the CRC cards show dependencies:
		<ul>
			<li><tt>Mailbox</tt> depends on <tt>MessageQueue</tt></li>
			<li><tt>MailSystem</tt> depends on <tt>Mailbox</tt></li>
			<li><tt>Connection</tt> depends on <tt>Telephone</tt>,
				<tt>MailSystem</tt>, <tt>Message</tt>, and <tt>Mailbox</tt></li>
			<li><tt>Telephone</tt> depends on <tt>Connection</tt></li>
		</ul>
	</li>
</ul>

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<hr><h2><font color="#009999">25.6.3 UML Class Diagrams for the Voice Mail
	System</font></h2>
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<hr><h2><font color="#009999">25.6.3 UML Class Diagrams for the Voice Mail
	System</font></h2>
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<ul>
	<li>Aggregation:
		<ul>
			<li>System has mailboxes</li>
			<li>Mailbox has 2 msg queues</li>
			<li>Queue has msgs (maybe)</li>
			<li>A <tt>Connection</tt> has a current mailbox; also references to the
				<tt>MailSystem</tt> and <tt>Telephone</tt> objects</li>
		</ul>
	</li>
	<li>No inheritance</li>
	<li>Note:  aggregation implies dependency</li>
</ul>

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<hr><h2><font color="#009999">25.6.3 UML Class Diagrams for the Voice Mail
	System</font></h2>
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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams</font></h2>
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<ul>
	<li>Understand complex control flow w/multiple objects</li>
	<li><tt>Telephone</tt> reads input</li>
	<li>Passes it to <tt>Connection</tt></li>
	<li>Postulate 3 functions for <tt>Connection</tt>:
		<ul>
			<li><tt>dial</tt> - passes on button press</li>
			<li><tt>record</tt> - passes on speech</li>
			<li><tt>hangup</tt> - tells connection telephone has hung up</li>
		</ul>
	</li>
</ul

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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams (cont.)
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<h3><b>Leave a Message</b> sequence diagram</h3>

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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams (cont.)
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<h3><b>Leave a Message</b> sequence diagram</h3>

<ol>
	<li>Caller keys in extension (shown as single call to <tt>dial</tt>)</li>
	<li><tt>Connection</tt> calls system's <tt>find_mailbox</tt></li>
	<li>The <tt>Mailbox</tt> object on the right is returned</li>
	<li>Connection invokes <tt>get_greeting</tt><br>
		(greeting is passive; doesn't appear on diagram)</li>
	<li>Connection plays appropriate greeting</li>
	<li>Telephone reads msg from user, passes it to connection</li>
	<li>Telephone reads hangup, passes it to connection</li>
	<li>Connection constructs <tt>Message</tt>, adds it to mailbox</li>
</ol>

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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams (cont.)
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<h3><b>Retrieve a Message</b> sequence diagram</h3>

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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams (cont.)
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<ul>
	<li>System is not in control of input</li>
	<li>Telephone notifies connection of any input event</li>
	<li>E.g., connection is called 3 times during <b>Leave a Msg</b></li>
	<li>The connection must keep track of states, to determine proper
		action on given input</li>
	<li>Next slide is the state diagram for the system</li>
</ul>

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<hr><h2><font color="#009999">25.6.4 UML Sequence and State Diagrams (cont.)
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<hr><h2><font color="#009999">25.6.5 Implementation</font></h2>
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<ul>
	<li>Following files can be downloaded and run</li>
	<li>Enter <tt>Q</tt> to quit</li>
	<li>Look at the classes</li>
	<li>Compare documentation to the CRC cards and UML diagrams</li>
	<li>Trace functions calls, compare to the sequence diagrams</li>
	<li>Find the state transitions for <tt>Connection</tt></li>
	<li>Only modify <tt>Telephone</tt> and <tt>MailSystemTest</tt> to add
		a GUI (chptr 27)</li>
</ul>

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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>message.h</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>mailbox.h</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>mailbox.cpp</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>mailsystem.h</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>mailsystem.cpp</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>telephone.h</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>telephone.cpp</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>connection.h</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation (<tt>connection.cpp</tt>)
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<hr><h2><font color="#009999">25.6.5 Implementation
	(<tt>mailsystemtest.cpp</tt>)</font></h2>
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<hr><h2><font color="#009999">Chapter Summary</font></h2>
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<ol>
	<li>Graphical notations help convey design information</li>
	<li>Use cases provide concrete scenarios from which general action can be
		abstracted</li>
	<li>Class diagrams record various relationships, including use, dependency,
			and inheritance</li>
	<li>Sequence diagrams record the dynamic interaction between objects</li>
	<li>State diagrams are useful for documenting objects that change their
		behavior during the course of execution according to their current
		state</li>
</ol>

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