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35 <h1>Using the Multiplexing Look and Feel</h1>
36
37 <blockquote>
38 <hr>
39 <p>
40 <i>
41 This document is based on an article
42 originally published in
43 <a href="http://www.oracle.com/technetwork/java/javase/tech/articles-jsp-139072.html"
44 target="_top"><em>The Swing Connection</em></a>.
45 </i>
46 </p>
47 <hr>
48 </blockquote>
49
50 <p>
51 The Multiplexing look and feel lets
52 you supplement an ordinary look and feel
53 (called the <em>default</em> look and feel)
54 with one or more <em>auxiliary</em> look and feels.
55 For example, you could
56 simultaneously provide text-to-speech and Braille outputs,
57 in addition to the ordinary visual output that a Swing-based
58 application generates,
59 by adding
60 two auxiliary look and feels (one for text-to-speech,
61 the other for Braille)
62 to the default look and feel.
63 The default look and feel can be any ordinary look and feel --
64 the Java or Windows look and feel, for example --
65 and requires no modifications to work with auxiliary look and feels.
66 </p>
67
68
69 <p>
70 This document has the following sections:
71 <ul>
72 <li> <a href="#overview">Overview</a>
73 <li> <a href="#howtouse">How to Use Auxiliary Look and Feels</a>
74 <li> <a href="#howtowrite">Tips for Writing an Auxiliary Look and Feel</a>
75 <ul>
76 <li> <a href="#dosanddonts">Dos and Don'ts</a>
77 <li> <a href="#uidefaults">Extending UIDefaults</a>
78 <li> <a href="#defaultui">Examining Other UI Objects</a>
79 </ul>
80 <li> <a href="#implementation">How the Multiplexing Look and Feel is
81 Implemented</a>
82 <li> <a href="#custom">How to Provide a Custom Multiplexing
83 Look and Feel</a>
84 </ul>
85
86 <p>
87 Before reading further, you should be familiar
88 with the concept of pluggable look and feels.
89 For basic information, see
90 <a href="https://docs.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html">
91 How to Set the Look and Feel</a>, a section in <em>The Java Tutorial</em>.
92 For architectural details, you can read
93 <a
94 href="http://www.oracle.com/technetwork/java/architecture-142923.html#pluggable">
95 Pluggable look-and-feel architecture</a>, a section within
96 a <em>Swing Connection</em> article.
97 </p>
98
99 <p>
100 <a id="overview"></a>
101 <hr>
102 <h2>Overview</h2>
103
104 <p>
105
106 The classes in the
107 <code>javax.swing.plaf.multi</code> package
108 implement a
109 <i>multiplexing look and feel</i>.
110 A multiplexing look and feel transparently creates -- and
111 simultaneously supports -- UI objects from several different look and feels
112 in response to a component requesting its UI object
113 (with the <code>getUI</code> method).
114
115 <p>
116 Without a multiplexing look and feel, a
117 developer who wanted to enhance a particular look and feel would
118 need to extend the classes supporting that look and feel. For example, to
119 add text-to-speech support to the Java look and feel without using a multiplexing
120 look and feel, the developer would need to create a group of
121 classes that extend those of
122 the Java look and feel, and add text-to-speech support to the new classes.
123 If the developer also wanted to add text-to-speech support to other look
124 and feels,
125 such as Motif or Windows, the developers would need to create subclasses
126 of those classes as well.
127 </p>
128
129 <p>
130 This approach has at least two shortcomings:
131 <ul>
132 <li>First, each subclass must use what is
133 essentially a copy of the same code, potentially creating a difficult
134 support situation for the developer.<br></li>
135 <li>Second, and more significantly for the
136 end user, some application developers might force a
137 particular look and feel to be used. When this approach is used,
138 the end user can't even use the enhanced look and feel.</li>
139 </ul>
140
141 <p>
142 A multiplexing look and feel
143 both these problems simultaneously because it allows multiple look
144 and feels to be combined.
145 The first problem (having to use what amounts to a second copy of the same
146 code) is solved because the developer can create a specialized look
147 and feel that can then be combined with other look and feels.
148 </p>
149
150 <p>
151 The second problem (having to force the use of
152 a particular look and feel) is solved because a specialized look and feel
153 can be used with whatever default look and feel the
154 application may have locked in place.
155 </p>
156
157 <p>
158 The default multiplexing look and feel implementation,
159 represented by the <code>MultiLookAndFeel</code> class
160 in the <code>javax.swing.plaf.multi</code> package,
161 is called (unsurprisingly)
162 the Multiplexing look and feel.
163
164 <p>
165 <a id="howtouse"></a>
166 <hr>
167 <h2>How to Use Auxiliary Look and Feels</h2>
168
169 <p>
170 It's easy to use auxiliary look and feels with Swing. To instruct
171 Swing to use the Multiplexing look and feel, all an application
172 has to do is modify the <code>$JDKHOME/conf/swing.properties</code>
173 file to include a definition of the <code>swing.auxiliarylaf</code>
174 property. Swing treats the <code>swing.auxiliarylaf</code>
175 property as a comma-separated list of <code>LookAndFeel</code>
176 subclasses that specify what auxiliary look and feels should be
177 used in addition to the default look and feel. If at least one valid
178 <code>LookAndFeel</code>
179 subclass is specified in the <code>swing.auxiliarylaf</code>
180 property, Swing automatically uses the Multiplexing look and feel
181 to load and support the default and auxiliary look and feels.
182 </p>
183
184 <p>
185 For example, let's assume that an application
186 makes use of a look and feel that supports text-to-speech feedback, and also
187 uses an look and feel that adds support for a device
188 that emits perfume.
189 Let's assume that the text-to-speech
190 look and feel is named <code>com.myco.TextTalkerLookAndFeel</code>,
191 and the look and feel that adds support for perfume
192 is named <code>com.smellco.OlfactoryLookAndFeel</code>.
193 </p>
194
195 <p>
196 To tell Swing to use both these look and feels
197 -- and to use a default look and feel at the same time -- your application
198 could simply add the following line to the <code>$JDKHOME/conf/swing.properties</code> file:
199 </p>
200
201 <p>
202 <code>
203 swing.auxiliarylaf=com.myco.TextTalkerLookAndFeel,<br>
204 com.smellco.OlfactoryLookAndFeel</code>
205 </p>
206
207 <p>
208 This statement tells Swing to obtain a component's UI from the Multiplexing
209 look and feel automatically, instead of obtaining it directly from
210 the default look and feel. The resulting multiplexing UI is a small
211 delegate that obtains and maintains UIs from the default and auxiliary
212 look and feels. As a result, when a method is invoked in a multiplexing
213 UI object, the multiplexing UI invokes the same method on each
214 of the UIs obtained from the default and auxiliary look and feels.
215 </p>
216
217 <p>
218 <a id="howtowrite"></a>
219 <hr>
220 <h2>Tips for Writing an Auxiliary Look and Feel</h2>
221
222 <p>
223 An auxiliary look and feel is like any other look and feel,
224 except that it doesn't have to provide the complete support
225 that a default look and feel must. For
226 example, an auxiliary look and feel that supports just text-to-speech feedback
227 doesn't need to provide any code for painting.
228 Also, it might not need to support all components --
229 <code>JSeparator</code>s, for example, might be ignored.
230
231 <p>
232 Auxiliary look and feels tend to be simple,
233 so developing one can be easier than developing a visual
234 look and feel.
235 The developer can concentrate solely
236 on providing the specialized functionality.
237
238 <p>
239 Because the primary purpose of an auxiliary look and feel is to enhance the
240 default look and feel, auxiliary look and feels tend
241 be nonvisual. Since an auxiliary look and feel is a genuine
242 look and feel, however, there is nothing to prevent it
243 from rendering information on the display.
244 </p>
245
246 <p>
247 Just like for any other look and feel, you
248 implement an auxiliary look and feel
249 by writing a subclass of <code>javax.swing.LookAndFeel</code>
250 and creating subclasses of the
251 <code><em>Foo</em>UI</code> classes defined in
252 the <code>javax.swing.plaf</code> package.
253 </p>
254
255 <a id="dosanddonts"></a>
256 <h3>Dos and Don'ts</h3>
257
258 <p>
259 The following paragraphs provide some general recommendations for developing
260 auxiliary look and feels.
261 </p>
262
263 <h4>Use the <code>installUI</code> method
264 to perform all initialization,
265 and the <code>uninstallUI</code> method
266 to perform all cleanup.</h4>
267
268 <blockquote>
269 The <code>installUI</code> and <code>uninstallUI</code>
270 methods are invoked when a component's look and feel is set.
271 The <code>installUI</code> method gives the new UI object
272 a chance to add listeners on the component and its data model.
273 Similarly, the <code>uninstallUI</code> method
274 lets the previous UI object remove its listeners.
275 </blockquote>
276 <h4><b>Don't extend visual look and feels.</b></h4>
277 <blockquote>
278 We recommended that you <i>don't</i> implement
279 UI classes of an auxiliary look and feel as subclasses of the
280 UI classes of a visual look and feel. Why not? Because they might
281 accidentally inherit code that installs listeners on a component
282 object or renders the component on the display. As a result,
283 your auxiliary look and feel would compete with the default look
284 and feel rather than cooperating with it.<br>
285 <br>
286 Instead, we recommend that the UI classes of an auxiliary look
287 and feel directly extend the abstract UI classes in the <code>javax.swing.plaf</code>
288 package. By using this strategy, the developer of an auxiliary
289 look and feel can avoid competing with the default look and feel.
290 </blockquote>
291 <h4><b>Override all UI-specific methods your UI classes inherit.</b></h4>
292
293 <blockquote>
294 We recommend that each UI class of
295 an auxiliary look and feel override the methods
296 defined in the <code>javax.swing.plaf</code>
297 UI classes it descends from
298 The reasons for this recommendation are similar
299 to those for not extending a visual look and feel.
300 For example, the <code>ComponentUI</code>
301 class, from which all UI classes descend,
302 provides a default implementation for the <code>update</code>
303 method. This default implementation paints on the display
304 if the
305 component is opaque. If a UI class from a non-visual auxiliary
306 look and feel does not override this method, all
307 opaque components appear as blank areas on the screen!
308 </blockquote>
309
310 <a id="uidefaults"></a>
311 <h3>Extending UIDefaults</h3>
312
313 <p>In many cases, you
314 might want an auxiliary look and feel to be "incomplete." That
315 is, you might not need to support the complete set
316 of components.
317 For example, an auxiliary look and feel might choose
318 to provide a <code>ButtonUI</code> subclass but no
319 <code>LabelUI</code> subclass.
320 This
321 option is allowed, and the multiplexing look and feel gracefully
322 handles such situations.</p>
323 <p>By default, however, Swing issues an error message when it asks
324 a look and feel for a UI object and the look and feel does not
325 support that UI. This message can be annoying, especially to auxiliary
326 look-and-feel developers who don't want to support a particular
327 component.</p>
328 <p>Fortunately, you can prevent this error
329 message by creating a subclass of the <code>UIDefaults</code>
330 class and returning an instance of it from the
331 <code>getDefaults</code> method
332 of your <code>LookAndFeel</code> class.
333 For example:
334 </p>
335 <p><code>public class MyAuxLookAndFeel
336 extends LookAndFeel {<br>
337 ...<br>
338 public UIDefaults getDefaults() {<br>
339 <b>UIDefaults table = <br>
340
341 new MyAuxUIDefaults();<br>
342 </b> Object[] uiDefaults = {<br>
343 "ButtonUI", "MyAuxButtonUI",<br>
344 ...<br>
345 }<br>
346 table.putDefaults(uiDefaults);<br>
347 return table;<br>
348 }<br>
349 }<br>
350 <br>
351 <b>class MyAuxUIDefaults extends UIDefaults {<br>
352 protected void getUIError(String msg) {<br>
353 //System.err.println<br>
354 // ("An
355 annoying message!");<br>
356 }<br>
357 }</b></code></p>
358
359 <p>
360 In the preceding example, an auxiliary look and feel named <code>MyAux</code>
361 creates a <code>UIDefaults</code> subclass
362 that overrides the <code>getUIError</code>
363 method. The <code>getUIError</code>
364 method is the method that is invoked when Swing cannot find a UI
365 object in a look and feel. By merely doing nothing in this method,
366 you can avoid the error message.</p>
367 <p>
368
369 <a id="defaultui"></a>
370 <h3>Examining Other UI Objects</h3>
371
372 <p>In
373 rare instances, a UI object from an auxiliary look and feel
374 may be interested in the default UI object used by the component. In
375 these cases, the UI object from auxiliary look and feel can obtain
376 the UI from a component by calling its <code>getUI</code>
377 method. The returned UI is an instance of one of the multiplexing
378 look and feel UI classes (for example, <code>MultiButtonUI</code>).
379 The UI object from the auxiliary look and feel can call the <code>getUIs</code>
380 method of the returned object to obtain an array containing a complete list
381 of all UI objects handled by the multiplexing UI. The first element
382 is guaranteed to be the UI created from the default look and feel.
383 </p>
384
385 <p>
386 <a id="implementation"></a>
387 <hr>
388 <h2>How the Multiplexing Look and Feel Is Implemented</h2>
389
390 <p>
391 The Multiplexing look and feel
392 (represented by
393 <code>javax.swing.plaf.multi.MultiLookAndFeel</code>)
394 is meant to be transparent to
395 all developers and users. It should "just work" -- and
396 it is used only when the user tells Swing to use an auxiliary look
397 and feel.</p>
398
399 <p>
400 When the Multiplexing look and
401 feel is in use, the type of the UI object
402 associated with each component
403 depends on whether
404 any of the auxiliary look and feels currently in use
405 support the component.
406 If so, the component's UI object is
407 an instance of a multiplexing UI.
408 If only the default look and feel supports the component,
409 then the component gets
410 a UI object from the default look and feel,
411 just as if no auxiliary look and feels were installed.
412
413 <p>
414 A multiplexing UI object
415 obtains and maintains UI objects
416 from the default and auxiliary look
417 and feels,
418 referring to these UIs in the following manner:
419
420 <ul>
421 <li> The UI object from the default look
422 and feel is always the first to be created. After that, a UI object
423 is created from each auxiliary look and feel in the order
424 they are specified in the <code>swing.auxiliarylaf</code>
425 property.<br><br></li>
426
427 <li> When a method that requests information
428 from a UI object is invoked, the multiplexing UI object
429 invokes the method on all the UI objects, but returns
430 only the results from the UI for the default look and feel.
431 For example, when the <code>getPreferredSize</code>
432 method is invoked on a multiplexing UI, the UI returns only the
433 results of invoking <code>getPreferredSize</code>
434 on the UI obtained from the default look and feel.
435 The <code>getPreferredSize</code> method
436 is also invoked on the UI object for each auxiliary look and feel,
437 but the return values are ignored.
438 <br><br></li>
439
440 <li> When a method that does not request information
441 from the UI object is invoked, the multiplexing UI object
442 invokes that method on all UIs --
443 on the UI object obtained from the default look
444 and feel
445 and on all the UIs obtained from the auxiliary look and feels,
446 as well.
447 For example, invoking the <code>installUI</code>
448 method on a multiplexing UI causes the multiplexing UI to invoke
449 <code>installUI</code>
450 on the UI obtained from the default look and feel and the UIs obtained from
451 the auxiliary factories.</li>
452 </ul>
453 <p> In all cases, the UI object obtained from
454 the default look and feel is acted upon first, and then the auxiliary
455 look and feels are acted upon in the order they are specified in
456 the <code>swing.auxiliarylaf</code>
457 property.
458 </p>
459
460 <p>
461
462 <a id="custom"></a>
463 <hr>
464 <h2>How to Provide a Custom Multiplexing Look and Feel</h2>
465
466 <p>While
467 we hope the behavior of the Multiplexing look and feel is
468 flexible enough not to require an alternative multiplexing look
469 and feel, Swing allows the user to specify another multiplexing look
470 and feel to use.
471 </p>
472
473 <p> To do that, all the user has to do is modify
474 the <code>$JDKHOME/conf/swing.properties</code>
475 file to include a definition of the <code>swing.plaf.multiplexinglaf</code>
476 property. Swing then treats the <code>swing.plaf.multiplexinglaf</code>
477 property as a <code>LookAndFeel</code>
478 subclass that supports multiplexing.
479 </p>
480 <p> For example, if a user has a multiplexing
481 look and feel represented by <code>com.myco.SuperMultiLookAndFeel</code>
482 that is a better match for their needs than the Multiplexing
483 look and feel
484 (<code>javax.swing.plaf.multi.MultiLookAndFeel</code>),
485 the user could include the following line in <code>$JDKHOME/conf/swing.properties</code>:
486 </p>
487
488 <p>
489 <code>swing.plaf.multiplexinglaf = com.myco.SuperMultiLookAndFeel</code>
490 </p>
491
492 <p>
493 This statement instructs Swing to use <code>com.myco.SuperMultiLookAndFeel</code>
494 instead of <code>javax.swing.plaf.multi.MultiLookAndFeel</code>. But
495 if you use this kind of statement, be careful, because the suppliers
496 of auxiliary look and feels will most likely have developed and
497 tested against our Multiplexing look and feel.
498 </p>
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