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<TITLE>Target Factory</TITLE>
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<H2>How to use the TargetFactory</H2>
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By <font color=0000FF><i>Elmar Grom</i></font>
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<br><br>
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Here is a simple approach that you can use to automatically instantiate
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flavors of your class that are tailored to a specific operating system.
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If necessary you can even have different versions for different flavors
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of an operating system, such as Windows-NT.
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<br><br>
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Implement your API with the class name that you would like to use. The
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API can be implemented as interface, a partially or completely abastact
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class or a complete class implementation. The choice is your's and
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primarily depends your specific needs. However, it seems likely that in
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most cases it will be necessary to have a default implementation that
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can be instantiated if an appropriate flavor does not exist for some
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reason. One situation might be that a special version is not needed for
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all the different OS/OS-Flavor combinations but only for one or two
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cases. For all other cases the default implementation might work just
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fine. Another reason would be that an installation is attempted on an OS
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that is unknown or is not listed and as a fallback position a default
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implementation of the class should be available. For the following I
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assume that a complete implementation is used.
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<br><br>
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In the next step you need to derive one class for each of the different
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flavors you want to support with specific implementations. All of these
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classes must be contained in the same package as the base class and must
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follow a prescribed naming convention. Name prefixes are defined for a
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number of operating systems and operating system flavores. Please review
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the class documentation for <code>TargetFactory</code> for a a complete
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list of these prefixes.
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<br><br>
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Let's assume you have a class called <code>MyClass</code> in the package
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<code>com.izforge.izpack.installer</code>. This class contains your
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default implementation. For some reason you need modified functionality
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for Mac OS X.  You would now implement the class
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<code>Mac_X_MyClass</code> which is extending <code>MyClass</code> and
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implements the necessary differences. This is all you need to do on the
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implementation end.
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<br><br>
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To get the correct instance based on the OS, simply call
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<code>makeObject()</code>. This example illustrates the call:<br>
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<PRE>
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  <font size=2 color=000000>TargetFactory.<b>getInstance</b> ().<b>makeObject</b> (</font><font size=2 color=FF0000>"com.izforge.izpack.installer.MyClass"</font><font size=2 color=000000>);</font>
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</PRE>
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This call will return an instance of the proper flavor, without worry
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about the OS on your part. More specifically, you will recive an
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instance of <code>MyClass</code> on all operating systems, except on Mac
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OS X, in which case you will  receive an instance of
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<code>Mac_X_MyClass</code>. To make this work,
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<code>TargetFactory</code> will automatically map the correct name and
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create an instance for you.
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<H3>The Constructor</H3>
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There is one drawback to this implementation that you must be aware of.
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Because of the way how instances are created, each class must have a
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default constructor. Of course this is done either by not implementing a
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constructor or by implementing a constructor without parameters (this
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must not be private). This constructor will be used when instances are
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created. As a result, you can not pass parameters to the constructor.
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<br><br>
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If you need to create instances that perform initial operations based on
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a set of parameters, I recommend the following approach. Instead of a
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constructor implement a method called <code>initialize()</code>. Call
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<code>makeObject()</code> to get your instance and then call
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<code>initialize()</code> with your parameters before using that object.
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