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《Big C++ 》Third Edition电子书和代码全集-Part1

<ul>
	<blockquote>
<pre>inline void ItemIterator::next()
{
   pos++;
}

bool ItemIterator::is_done() const
{
   return pos &gt;= items.size();
}</pre>
		</blockquote>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study:  Putting Patterns to Work (cont.)
	</font></h2>
<font size="+1">

<ul>
	<li>Consider the current format of the invoice:
		<script><!--
			image( "un08.png" )
		//--></script>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study:  Putting Patterns to Work (cont.)
	</font></h2>
<font size="+1">

<ul>
	<li>Sufficient for all applications?</li>
	<li>Printing a Web page?  Need HTML tags</li>
	<li>Need multiple algorithms for formatting</li>
	<li>Use STRATEGY pattern</li>
	<li>Design i/f to abstract out essential steps of the algorithm:
		<ul>
			<li>Print header</li>
			<li>Print footer</li>
			<li>Print column entry (string or number)</li>
		</ul>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study:  Putting Patterns to Work (cont.)
	</font></h2>
<font size="+1">

<ul>
	<li>The i/f:
		<blockquote>
<pre>class InvoicePrinter
{
public:
   virtual void print_header(string s) = 0;
   virtual void print_string(string value, bool pad_right) = 0;
   virtual void print_number(double value, int precision) = 0;
   virtual void print_footer(string s, double total) = 0;
};</pre>
		</blockquote>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study:  Putting Patterns to Work (cont.)
	</font></h2>
<font size="+1">

<ul>
	<li>Make the strategy object available to <tt>Invoice::print</tt>:
		<blockquote>
<pre>
void Invoice::print(InvoiceFormatter&amp; formatter)
{
   print_header("I N V O I C E");
   print_string("Description", true);
   print_string("Unit Price", false);
   print_string("Qty", false);
   print_string("Total Price", false);

   double amount_due = 0;
   for (ItemIterator iter = inv.create_iterator();
      !iter.is_done(); iter.next())
   {
      Item* it = iter.get();
      print_string(it-&gt;get_description(), true);
      print_number(it-&gt;get_unit_price(), 2);
      print_number(it-&gt;get_quantity(), 0);
      print_number(it-&gt;get_total_price(), 2);
      amount_due = amount_due + it-&gt;get_total_price();
   }

   print_footer("AMOUNT DUE:", amount_due);
}</pre>
		</blockquote>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study:  Putting Patterns to Work (cont.)
	</font></h2>
<font size="+1">

<ul>
	<li>Relationships between classes for formatting:
		<script><!--
			image( "fig05.png" )
		//--></script>
	</li>
</ul>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>product.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "product.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>item.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "item.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>productitem.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "productitem.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>bundle.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "bundle.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>itemiterator.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "itemiterator.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>invoiceprinter.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "invoiceprinter.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>simpleinvoiceprinter.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "simpleinvoiceprinter.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>invoice.h</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "invoice.h", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>product.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "product.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>item.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "item.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>productitem.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "productitem.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>bundle.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "bundle.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>itemiterator.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "itemiterator.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study:
	(<tt>simpleinvoiceprinter.cpp</tt>)</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "simpleinvoiceprinter.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>invoice.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "invoice.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">26.7 Case Study: (<tt>invoicetest.cpp</tt>)
	</font></h2>
<font size="+1">

<script><!-- 
	iframeWrapCode( "invoicetest.cpp", "95%", "80%" )
//--></script>

</font>

<hr><h2><font color="#009999">More Patterns</font></h2>
<font size="+1">

<p>Quick table of patterns from <u>Design Patterns</u>:</p>

<table border='1' cellpadding='4'>
	<tr bgcolor='#00ffff'>
		<th>Pattern Name</th>
		<th>Description</th>
		<th>Example</th>
	</tr>
	<tr>
		<th>Abstract Factory</th>
		<td>An abstract class defines methods that construct related products.
			Concrete factories create these product sets</td>
		<td>An abstract class specifies methods for constructing buttons, methods,
			and so on. Each user interface look and feel supplies a concrete
			subclass</td>
	</tr>
	<tr>
		<th>Bridge</th>
		<td>An abstraction and its implementation have separate inheritance
			hierarchies</td>
		<td>A hierarchy of window types has separate implementations in various
			operating systems</td>
	</tr>
	<tr>
		<th>Builder</th>
		<td>A builder class has methods to build parts of a complex product, and to
			retrieve the completed product</td>
		<td>A document builder has methods to build paragraphs, tables, and so
			on</td>
	</tr>
</table>
</font>

<hr><h2><font color="#009999">More Patterns (cont.)</font></h2>
<font size="+1">

<table border='1' cellpadding='4'>
	<tr bgcolor='#00ffff'>
		<th>Pattern Name</th>
		<th>Description</th>
		<th>Example</th>
	</tr>
	<tr>
		<th>Chain of Responsibility</th>
		<td>A request is passed to the first handler in a chain. Each handler acts
			on the request (or chooses not to act), and passes the request on to the
			next handler</td>
		<td>An event-handling mechanism passes a mouse or key event to a component,
			which then passes it to the parent component</td>
	</tr>
	<tr>
	<th>Command</th>
		<td>Commands are implemented as objects</td>
		<td>A word processor stores recently issued commands so that they can be
			undone</td>
	</tr>
	<tr>
		<th>Decorator</th>
		<td>The behavior of a class is enhanced, keeping its interface</td>
		<td>A user interface component is decorated with scroll bars or borders</td>
	</tr>
	<tr>
		<th>Facade</th>
		<td>A complex subsystem is accessed through a single class</td>
		<td>A driver class provides access to the functionality of a database
			system</td>
	</tr>
</table>
</font>

<hr><h2><font color="#009999">More Patterns (cont.)</font></h2>
<font size="+1">

<table border='1' cellpadding='4'>
	<tr bgcolor='#00ffff'>
		<th>Pattern Name</th>
		<th>Description</th>
		<th>Example</th>
	</tr>
	<tr>
		<th>Factory Method</th>
		<td>A virtual constructor can be redefined by derived classes</td>
		<td>Collection classes that derive from a common base class redefine the
			create_iterator function</td>
	</tr>
	<tr>
		<th>Flyweight</th>
		<td>Uses shared objects instead of large numbers of separate objects with
			identical state</td>
		<td>A word processor uses shared objects for styled characters rather than a
			separate object for each character</td>
	</tr>
	<tr>
		<th>Interpreter</th>
		<td>A class hierarchy represents grammar rules. The interpreter recursively
			evaluates a parse tree of rule objects</td>
		<td>A program interactively evaluates mathematical expressions by building
			and evaluating a parse tree</td>
	</tr>
</table>
</font>

<hr><h2><font color="#009999">More Patterns (cont.)</font></h2>
<font size="+1">

<table border='1' cellpadding='4'>
	<tr bgcolor='#00ffff'>
		<th>Pattern Name</th>
		<th>Description</th>
		<th>Example</th>
	</tr>
	<tr>
		<th>Mediator</th>
		<td>An object encapsulates the interaction of other objects</td>
		<td>All components in a dialog box notify a mediator of state changes. The
			mediator updates affected components</td>
	</tr>
	<tr>
		<th>Memento</th>
		<td>An object yields an opaque snapshot of a part of its state, and can
			later return its state from that snapshot</td>
		<td>An undo mechanism requests a memento from an object before mutating it.
			If the operation is undone, the memento is used to roll the object back
			to its old state</td>
	</tr>
	<tr>
		<th>Observer</th>
		<td>An object wants to be notified when another object generates an
			event</td>
		<td>User interface components generate events, such as button clicks and
			text changes. A dialog box observes the events and repaints its
			contents</td>
	</tr>
</table>
</font>

<hr><h2><font color="#009999">More Patterns (cont.)</font></h2>
<font size="+1">

<table border='1' cellpadding='4'>
	<tr bgcolor='#00ffff'>
		<th>Pattern Name</th>
		<th>Description</th>
		<th>Example</th>
	</tr>
	<tr>
		<th>Proxy</th>
		<td>A service needs to be made more versatile without affecting the service
			provider or client</td>
		<td>A proxy class sends client requests to a server object on a different
			computer</td>
	</tr>
	<tr>
		<th>Singleton</th>
		<td>All clients need access to a single shared object of a class</td>
		<td>A random number singleton gives all clients access to the same
			generator</td>
	</tr>
	<tr>
		<th>State</th>
		<td>A separate object is used for each state. State-dependent code is
			distributed over the various state classes</td>
		<td>An image editor has different drawing states. Each state is handled by
			a separate tool object</td>
	</tr>
	<tr>
		<th>Visitor</th>
		<td>A structure with a fixed set of element classes needs an extensible set
			of operations</td>
		<td>An XML visitor visits a tree of XML elements, applying arbitrary
			operations to each node</td>
	</tr>
</table>

</font>

<hr><h2><font color="#009999">Chapter Summary</font></h2>
<font size="+1">
<hr color="#00ffff" size="6">

<ol>
	<li>Iterators are preferred to cursors</li>
	<li>A design pattern uses a standard format to give proven advice about a
		problem in software design</li>
	<li>The ITERATOR pattern teaches how to access the elements of an aggregate
		object</li>
	<li>The ADAPTER pattern teaches how to use a class in a context that requires
		a different interface</li>
	<li>The STRATEGY pattern teaches how to supply variants of an algorithm to a
		client</li>
	<li>The TEMPLATE METHOD pattern teaches how to supply varying behavior
		patterns to an algorithm</li>
	<li>The COMPOSITE pattern teaches how to combine several objects into an
		object that has the same behavior as its parts</li>
	<li>Design patterns apply in specific situations that are described by the
		context and solution parts of the pattern</li>
</ol>

</font>

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