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<TITLE>Using the Multiplexing Look and Feel</TITLE>
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<b>
<font size=+3>
Using the Multiplexing Look and Feel
</font>
</b>

<blockquote>
<hr>
<i>
<p>
This document is based on an article
originally published in
<a href="http://java.sun.com/products/jfc/tsc/" target="_top"><em>The Swing
Connection</em></a>.
</p>
</i>
<hr>
</blockquote>

<p>
The Multiplexing look and feel lets
you supplement an ordinary look and feel
(called the <em>default</em> look and feel)
with one or more <em>auxiliary</em> look and feels.
For example, you could
simultaneously provide text-to-speech and Braille outputs, 
in addition to the ordinary visual output that a Swing-based 
application generates,
by adding 
two auxiliary look and feels (one for text-to-speech,
the other for Braille)
to the default look and feel.
The default look and feel can be any ordinary look and feel --
the Java or Windows look and feel, for example --
and requires no modifications to work with auxiliary look and feels.
</p>

</p>

<p>
This document has the following sections:
<ul>
<li> <a href="#overview">Overview</a>
<li> <a href="#howtouse">How to Use Auxiliary Look and Feels</a>
<li> <a href="#howtowrite">Tips for Writing an Auxiliary Look and Feel</a>
     <ul>
     <li> <a href="#dosanddonts">Dos and Don'ts</a>
     <li> <a href="#uidefaults">Extending UIDefaults</a>
     <li> <a href="#defaultui">Examining Other UI Objects</a>
     </ul>
<li> <a href="#implementation">How the Multiplexing Look and Feel is
     Implemented</a>
<li> <a href="#custom">How to Provide a Custom Multiplexing
     Look and Feel</a>
</ul>

<p>
Before reading further, you should be familiar 
with the concept of pluggable look and feels.
For basic information, see
<a href="http://java.sun.com/docs/books/tutorial/uiswing/start/swingTour.html#plaf">Choosing the Look and Feel</a>,
a section in 
<em>The Java Tutorial</em>.
For architectural details, you can read
<a
href="http://java.sun.com/products/jfc/tsc/articles/architecture/#pluggable">Pluggable look-and-feel architecture</a>, a section within
a <em>Swing Connection</em> article.
</p>

<p> 
<a name="overview">
<hr width=100% align=LEFT size=2>
</a>
<b>
<font color="#000080" size="+2">Overview</font>
</b>

<p></p>

<p>

The classes in the 
<code>javax.swing.plaf.multi</code> package
implement a 
<i>multiplexing look and feel</i>.
A multiplexing look and feel transparently creates -- and 
simultaneously supports -- UI objects from several different look and feels
in response to a component requesting its UI object
(with the <code>getUI</code> method).

<p>
Without a multiplexing look and feel, a 
developer who wanted to enhance a particular look and feel would 
need to extend the classes supporting that look and feel. For example, to 
add text-to-speech support to the Java look and feel without using a multiplexing 
look and feel, the developer would need to create a group of
classes that extend those of
the Java look and feel, and add text-to-speech support to the new classes. 
If the developer also wanted to add text-to-speech support to other look
and feels, 
such as Motif or Windows, the developers would need to create subclasses 
of those classes as well.
</p>

<p>
This approach has at least two shortcomings: 
<ul type="DISC">
  <li>First, each subclass must use what is 
      essentially a copy of the same code, potentially creating a difficult 
      support situation for the developer.<br></li>
  <li>Second, and more significantly for the 
      end user, some application developers might force a
      particular look and feel to be used. When this approach is used, 
      the end user can't even use the enhanced look and feel.</li>
</ul>

<p>
A multiplexing look and feel 
both these problems simultaneously because it allows multiple look 
and feels to be combined.
The first problem (having to use what amounts to a second copy of the same 
code) is solved because the developer can create a specialized look 
and feel that can then be combined with other look and feels.
</p>

<p>
The second problem (having to force the use of 
a particular look and feel) is solved because a specialized look and feel 
can be used with whatever default look and feel the 
application may have locked in place.
</p>

<p>
The default multiplexing look and feel implementation, 
represented by the <code>MultiLookAndFeel</code> class
in the <code>javax.swing.plaf.multi</code> package,
is called (unsurprisingly) 
the Multiplexing look and feel.

<p> 
<a name="howtouse">
<hr width=100% align=LEFT size=2>
</a>
<b>
<font color="#000080" size="+2">How to Use Auxiliary Look and Feels</font>
</b>

<p></p>

<p>
It's easy to use auxiliary look and feels with Swing. To instruct 
Swing to use the Multiplexing look and feel, all an application 
has to do is modify the <code>$JDKHOME/lib/swing.properties</code>
file to include a definition of the <code>swing.auxiliarylaf</code>
property. Swing treats the <code>swing.auxiliarylaf</code>
property as a comma-separated list of <code>LookAndFeel</code>
subclasses that specify what auxiliary look and feels should be 
used in addition to the default look and feel. If at least one valid 
<code>LookAndFeel</code>
subclass is specified in the <code>swing.auxiliarylaf</code>
property, Swing automatically uses the Multiplexing look and feel 
to load and support the default and auxiliary look and feels.
</p>

<p>
For example, let's assume that an application 
makes use of a look and feel that supports text-to-speech feedback, and also 
uses an look and feel that adds support for a device
that emits perfume.
Let's assume that the text-to-speech
look and feel is named <code>com.myco.TextTalkerLookAndFeel</code>, 
and the look and feel that adds support for perfume
is named <code>com.smellco.OlfactoryLookAndFeel</code>.
</p>

<p>
To tell Swing to use both these look and feels 
-- and to use a default look and feel at the same time -- your application 
could simply add the following line to the <code>$JDKHOME/lib/swing.properties</code> file:
</p>

<p>
<code>&nbsp;&nbsp;&nbsp; 
              swing.auxiliarylaf=com.myco.TextTalkerLookAndFeel,<br>
              &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; com.smellco.OlfactoryLookAndFeel</code>
</p>

<p>
This statement tells Swing to obtain a component's UI from the Multiplexing 
look and feel automatically, instead of obtaining it directly from 
the default look and feel. The resulting multiplexing UI is a small 
delegate that obtains and maintains UIs from the default and auxiliary 
look and feels. As a result, when a method is invoked in a multiplexing 
UI object, the multiplexing UI invokes the same method on each 
of the UIs obtained from the default and auxiliary look and feels.
</p>

<p> 
<a name="howtowrite">
<hr width=100% align=LEFT size=2>
</a>
<b>
<font color="#000080" size="+2">Tips for Writing an Auxiliary Look and Feel</font>
</b>

<p></p>

<p>
An auxiliary look and feel is like any other look and feel,
except that it doesn't have to provide the complete support 
that a default look and feel must. For 
example, an auxiliary look and feel that supports just text-to-speech feedback 
doesn't need to provide any code for painting. 
Also, it might not need to support all components --
<code>JSeparator</code>s, for example, might be ignored.

<p>
Auxiliary look and feels tend to be simple,
so developing one can be easier than developing a visual 
look and feel.
The developer can concentrate solely 
on providing the specialized functionality. 

<p>
Because the primary purpose of an auxiliary look and feel is to enhance the 
default look and feel, auxiliary look and feels tend 
be nonvisual. Since an auxiliary look and feel is a genuine
look and feel, however, there is nothing to prevent it
from rendering information on the display.
</p>

<p>
Just like for any other look and feel, you
implement an auxiliary look and feel
by writing a subclass of <code>javax.swing.LookAndFeel</code>
and creating subclasses of the 
<code><em>Foo</em>UI</code> classes defined in
the <code>javax.swing.plaf</code> package.
</p>

<p> 
<br>
<a name="dosanddonts">
<font color="#000080" size="+1"><b>Dos and Don'ts</b></font> 
</a>
</p>
<p></p>

<p>
The following paragraphs provide some general recommendations for developing 
auxiliary look and feels.
</p>

<p>
<font color="#000080"><b>Use the <code>installUI</code> method
to perform all initialization,
and the <code>uninstallUI</code> method
to perform all cleanup.</b></font>
</font>
</p>
<ul>
<p>
The <code>installUI</code> and <code>uninstallUI</code>
methods are invoked when a component's look and feel is set.
The <code>installUI</code> method gives the new UI object
a chance to add listeners on the component and its data model.
Similarly, the <code>uninstallUI</code> method
lets the previous UI object remove its listeners.
</p>
            </ul>
            <p> <font color="#000080"><b>Don't extend 
              visual look and feels.</b></font></p>
            <ul>
              <p> We recommended that you <i>don't</i> implement 
                UI classes of an auxiliary look and feel as subclasses of the 
                UI classes of a visual look and feel. Why not? Because they might 
                accidentally inherit code that installs listeners on a component 
                object or renders the component on the display. As a result, 
                your auxiliary look and feel would compete with the default look 
                and feel rather than cooperating with it.<br>
                <br>
                Instead, we recommend that the UI classes of an auxiliary look 
                and feel directly extend the abstract UI classes in the <code>javax.swing.plaf</code> 
                package. By using this strategy, the developer of an auxiliary 
                look and feel can avoid competing with the default look and feel.</p>
            </ul>
            <p> <font color="#000080"><b>Override all UI-specific methods
	    your UI classes inherit.</b></font>
	    </p>
            <ul>
              <p> We recommend that each UI class of 
                an auxiliary look and feel override the methods 
		defined in the <code>javax.swing.plaf</code>
                UI classes it descends from
		The reasons for this recommendation are similar 
                to those for not extending a visual look and feel.
                For example, the <code>ComponentUI</code>
                class, from which all UI classes descend,
		provides a default implementation for the <code>update</code>
                method. This default implementation paints on the display
		if the 
                component is opaque. If a UI class from a non-visual auxiliary 
                look and feel does not override this method, all 
                opaque components appear as blank areas on the screen!</p>
            </ul>
            <p> 

<br>
<a name="uidefaults">
<font color="#000080" size="+1"><b>Extending UIDefaults</b></font> 
</a>
            <p></p>

            <p>In many cases, you 
              might want an auxiliary look and feel to be &quot;incomplete.&quot; That 
              is, you might not need to support the complete set 
              of components.
            For example, an auxiliary look and feel might choose 
	    to provide a <code>ButtonUI</code> subclass but no 
              <code>LabelUI</code> subclass.
	     This 
              option is allowed, and the multiplexing look and feel gracefully 
              handles such situations.</p>
            <p>By default, however, Swing issues an error message when it asks 
              a look and feel for a UI object and the look and feel does not 
              support that UI. This message can be annoying, especially to auxiliary 
              look-and-feel developers who don't want to support a particular 
              component.</p>
            <p>Fortunately, you can prevent this error 
              message by creating a subclass of the <code>UIDefaults</code> 
              class and returning an instance of it from the 
	      <code>getDefaults</code> method
	      of your <code>LookAndFeel</code> class.
	      For example:
	      </p>
            <p><code>public class MyAuxLookAndFeel 
              extends LookAndFeel {<br>
                  ...<br>
                  public UIDefaults getDefaults() {<br>
                      <b>UIDefaults table = <br>
              &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
              new MyAuxUIDefaults();<br>
              </b>        Object[] uiDefaults = {<br>
                        &quot;ButtonUI&quot;, &quot;MyAuxButtonUI&quot;,<br>
                        ...<br>
                      }<br>
                      table.putDefaults(uiDefaults);<br>
                      return table;<br>
                  }<br>
              }<br>
              <br>
              <b>class MyAuxUIDefaults extends UIDefaults {<br>
                  protected void getUIError(String msg) {<br>
                      //System.err.println<br>
              &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //&nbsp;&nbsp; (&quot;An 
              annoying message!&quot;);<br>
                  }<br>
              }</b></code></p>

<p>
In the preceding example, an auxiliary look and feel named <code>MyAux</code> 
              creates a <code>UIDefaults</code> subclass 
              that overrides the <code>getUIError</code> 
              method. The <code>getUIError</code> 
              method is the method that is invoked when Swing cannot find a UI 
              object in a look and feel. By merely doing nothing in this method, 
              you can avoid the error message.</p>
            <p> 

<br>
<a name="defaultui">
<b><font color="#000080" size="+1">Examining Other UI Objects</font></b> 
</a>
<p></p>

            <p>In 
              rare instances, a UI object from an auxiliary look and feel 
              may be interested in the default UI object used by the component. In 
              these cases, the UI object from auxiliary look and feel can obtain 
              the UI from a component by calling its <code>getUI</code>
              method. The returned UI is an instance of one of the multiplexing 
              look and feel UI classes (for example, <code>MultiButtonUI</code>). 
              The UI object from the auxiliary look and feel can call the <code>getUIs</code> 
              method of the returned object to obtain an array containing a complete list 
              of all UI objects handled by the multiplexing UI. The first element 
              is guaranteed to be the UI created from the default look and feel.
	      </p>

<p> 
<a name="implementation">
<hr width=100% align=LEFT size=2>
</a>
<font color="#000080" size="+2"><b>How the Multiplexing Look and Feel
Is Implemented</b></font> 
<p></p>

<p>
The Multiplexing look and feel
(represented by
<code>javax.swing.plaf.multi.MultiLookAndFeel</code>)
is meant to be transparent to 
all developers and users. It should &quot;just work&quot; -- and 
              it is used only when the user tells Swing to use an auxiliary look 
              and feel.</p>

            <p>
              When the Multiplexing look and 
              feel is in use, the type of the UI object 
	      associated with each component 
	      depends on whether 
	      any of the auxiliary look and feels currently in use
	      support the component.
	      If so, the component's UI object is
	      an instance of a multiplexing UI.
	      If only the default look and feel supports the component,
	      then the component gets
              a UI object from the default look and feel,
	      just as if no auxiliary look and feels were installed. 

	      <p>
	      A multiplexing UI object
              obtains and maintains UI objects
	      from the default and auxiliary look
	      and feels,
              referring to these UIs in the following manner: 

<ul type="DISC">
              <li> The UI object from the default look 
                and feel is always the first to be created. After that, a UI object 
                is created from each auxiliary look and feel in the order 
                they are specified in the <code>swing.auxiliarylaf</code> 
                property.</li>
<p>
              <li> When a method that requests information 
                from a UI object is invoked, the multiplexing UI object 
		invokes the method on all the UI objects, but returns 
                only the results from the UI for the default look and feel.
                For example, when the <code>getPreferredSize</code> 
                method is invoked on a multiplexing UI, the UI returns only the 
                results of invoking <code>getPreferredSize</code> 
                on the UI obtained from the default look and feel.
		The <code>getPreferredSize</code> method
		is also invoked on the UI object for each auxiliary look and feel,
		but the return values are ignored.
                </li>
<p>
              <li> When a method that does not request information 
                from the UI object is invoked, the multiplexing UI object 
                invokes that method on all UIs --
		on the UI object obtained from the default look
		and feel
                and on all the UIs obtained from the auxiliary look and feels,
		as well. 
                For example, invoking the <code>installUI</code> 
                method on a multiplexing UI causes the multiplexing UI to invoke 
                <code>installUI</code> 
                on the UI obtained from the default look and feel and the UIs obtained from 
                the auxiliary factories.</li>
            </ul>
            <p> In all cases, the UI object obtained from 
              the default look and feel is acted upon first, and then the auxiliary 
              look and feels are acted upon in the order they are specified in 
              the <code>swing.auxiliarylaf</code> 
              property.
</p>

<p> 

<a name="custom">
<hr width=100% align=LEFT size=2>
</a>
<font color="#000080" size="+2"><b>How to Provide a Custom Multiplexing Look
and Feel</b></font> 
<p></p>

            <p><font color="#000080" size="+2"><b></b></font>While 
              we hope the behavior of the Multiplexing look and feel is 
              flexible enough not to require an alternative multiplexing look 
              and feel, Swing allows the user to specify another multiplexing look 
              and feel to use.
</p>

            <p> To do that, all the user has to do is modify 
              the <code>$JDKHOME/lib/swing.properties</code> 
              file to include a definition of the <code>swing.plaf.multiplexinglaf</code> 
              property. Swing then treats the <code>swing.plaf.multiplexinglaf</code> 
              property as a <code>LookAndFeel</code> 
              subclass that supports multiplexing.
</p>
            <p> For example, if a user has a multiplexing 
              look and feel represented by <code>com.myco.SuperMultiLookAndFeel</code> 
              that is a better match for their needs than the Multiplexing 
              look and feel 
	      (<code>javax.swing.plaf.multi.MultiLookAndFeel</code>), 
              the user could include the following line in <code>$JDKHOME/lib/swing.properties</code>:
</p>

<p>
<code>swing.plaf.multiplexinglaf = com.myco.SuperMultiLookAndFeel</code>
</p>

<p>
This statement instructs Swing to use <code>com.myco.SuperMultiLookAndFeel</code> 
instead of <code>javax.swing.plaf.multi.MultiLookAndFeel</code>. But 
if you use this kind of statement, be careful, because the suppliers 
of auxiliary look and feels will most likely have developed and 
tested against our Multiplexing look and feel.
</p>

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