1 /*
2 * Copyright 1995-2006 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.awt;
27
28 import java.awt.peer.ButtonPeer;
29 import java.util.EventListener;
30 import java.awt.event;
31 import java.io.ObjectOutputStream;
32 import java.io.ObjectInputStream;
33 import java.io.IOException;
34 import javax.accessibility;
35
36 /**
37 * This class creates a labeled button. The application can cause
38 * some action to happen when the button is pushed. This image
39 * depicts three views of a "<code>Quit</code>" button as it appears
40 * under the Solaris operating system:
41 * <p>
42 * <img src="doc-files/Button-1.gif" alt="The following context describes the graphic"
43 * ALIGN=center HSPACE=10 VSPACE=7>
44 * <p>
45 * The first view shows the button as it appears normally.
46 * The second view shows the button
47 * when it has input focus. Its outline is darkened to let the
48 * user know that it is an active object. The third view shows the
49 * button when the user clicks the mouse over the button, and thus
50 * requests that an action be performed.
51 * <p>
52 * The gesture of clicking on a button with the mouse
53 * is associated with one instance of <code>ActionEvent</code>,
54 * which is sent out when the mouse is both pressed and released
55 * over the button. If an application is interested in knowing
56 * when the button has been pressed but not released, as a separate
57 * gesture, it can specialize <code>processMouseEvent</code>,
58 * or it can register itself as a listener for mouse events by
59 * calling <code>addMouseListener</code>. Both of these methods are
60 * defined by <code>Component</code>, the abstract superclass of
61 * all components.
62 * <p>
63 * When a button is pressed and released, AWT sends an instance
64 * of <code>ActionEvent</code> to the button, by calling
65 * <code>processEvent</code> on the button. The button's
66 * <code>processEvent</code> method receives all events
67 * for the button; it passes an action event along by
68 * calling its own <code>processActionEvent</code> method.
69 * The latter method passes the action event on to any action
70 * listeners that have registered an interest in action
71 * events generated by this button.
72 * <p>
73 * If an application wants to perform some action based on
74 * a button being pressed and released, it should implement
75 * <code>ActionListener</code> and register the new listener
76 * to receive events from this button, by calling the button's
77 * <code>addActionListener</code> method. The application can
78 * make use of the button's action command as a messaging protocol.
79 *
80 * @author Sami Shaio
81 * @see java.awt.event.ActionEvent
82 * @see java.awt.event.ActionListener
83 * @see java.awt.Component#processMouseEvent
84 * @see java.awt.Component#addMouseListener
85 * @since JDK1.0
86 */
87 public class Button extends Component implements Accessible {
88
89 /**
90 * The button's label. This value may be null.
91 * @serial
92 * @see #getLabel()
93 * @see #setLabel(String)
94 */
95 String label;
96
97 /**
98 * The action to be performed once a button has been
99 * pressed. This value may be null.
100 * @serial
101 * @see #getActionCommand()
102 * @see #setActionCommand(String)
103 */
104 String actionCommand;
105
106 transient ActionListener actionListener;
107
108 private static final String base = "button";
109 private static int nameCounter = 0;
110
111 /*
112 * JDK 1.1 serialVersionUID
113 */
114 private static final long serialVersionUID = -8774683716313001058L;
115
116
117 static {
118 /* ensure that the necessary native libraries are loaded */
119 Toolkit.loadLibraries();
120 if (!GraphicsEnvironment.isHeadless()) {
121 initIDs();
122 }
123 }
124
125 /**
126 * Initialize JNI field and method IDs for fields that may be
127 * accessed from C.
128 */
129 private static native void initIDs();
130
131 /**
132 * Constructs a button with an empty string for its label.
133 *
134 * @exception HeadlessException if GraphicsEnvironment.isHeadless()
135 * returns true
136 * @see java.awt.GraphicsEnvironment#isHeadless
137 */
138 public Button() throws HeadlessException {
139 this("");
140 }
141
142 /**
143 * Constructs a button with the specified label.
144 *
145 * @param label a string label for the button, or
146 * <code>null</code> for no label
147 * @exception HeadlessException if GraphicsEnvironment.isHeadless()
148 * returns true
149 * @see java.awt.GraphicsEnvironment#isHeadless
150 */
151 public Button(String label) throws HeadlessException {
152 GraphicsEnvironment.checkHeadless();
153 this.label = label;
154 }
155
156 /**
157 * Construct a name for this component. Called by getName() when the
158 * name is null.
159 */
160 String constructComponentName() {
161 synchronized (Button.class) {
162 return base + nameCounter++;
163 }
164 }
165
166 /**
167 * Creates the peer of the button. The button's peer allows the
168 * application to change the look of the button without changing
169 * its functionality.
170 *
171 * @see java.awt.Toolkit#createButton(java.awt.Button)
172 * @see java.awt.Component#getToolkit()
173 */
174 public void addNotify() {
175 synchronized(getTreeLock()) {
176 if (peer == null)
177 peer = getToolkit().createButton(this);
178 super.addNotify();
179 }
180 }
181
182 /**
183 * Gets the label of this button.
184 *
185 * @return the button's label, or <code>null</code>
186 * if the button has no label.
187 * @see java.awt.Button#setLabel
188 */
189 public String getLabel() {
190 return label;
191 }
192
193 /**
194 * Sets the button's label to be the specified string.
195 *
196 * @param label the new label, or <code>null</code>
197 * if the button has no label.
198 * @see java.awt.Button#getLabel
199 */
200 public void setLabel(String label) {
201 boolean testvalid = false;
202
203 synchronized (this) {
204 if (label != this.label && (this.label == null ||
205 !this.label.equals(label))) {
206 this.label = label;
207 ButtonPeer peer = (ButtonPeer)this.peer;
208 if (peer != null) {
209 peer.setLabel(label);
210 }
211 testvalid = true;
212 }
213 }
214
215 // This could change the preferred size of the Component.
216 if (testvalid && valid) {
217 invalidate();
218 }
219 }
220
221 /**
222 * Sets the command name for the action event fired
223 * by this button. By default this action command is
224 * set to match the label of the button.
225 *
226 * @param command a string used to set the button's
227 * action command.
228 * If the string is <code>null</code> then the action command
229 * is set to match the label of the button.
230 * @see java.awt.event.ActionEvent
231 * @since JDK1.1
232 */
233 public void setActionCommand(String command) {
234 actionCommand = command;
235 }
236
237 /**
238 * Returns the command name of the action event fired by this button.
239 * If the command name is <code>null</code> (default) then this method
240 * returns the label of the button.
241 */
242 public String getActionCommand() {
243 return (actionCommand == null? label : actionCommand);
244 }
245
246 /**
247 * Adds the specified action listener to receive action events from
248 * this button. Action events occur when a user presses or releases
249 * the mouse over this button.
250 * If l is null, no exception is thrown and no action is performed.
251 * <p>Refer to <a href="doc-files/AWTThreadIssues.html#ListenersThreads"
252 * >AWT Threading Issues</a> for details on AWT's threading model.
253 *
254 * @param l the action listener
255 * @see #removeActionListener
256 * @see #getActionListeners
257 * @see java.awt.event.ActionListener
258 * @since JDK1.1
259 */
260 public synchronized void addActionListener(ActionListener l) {
261 if (l == null) {
262 return;
263 }
264 actionListener = AWTEventMulticaster.add(actionListener, l);
265 newEventsOnly = true;
266 }
267
268 /**
269 * Removes the specified action listener so that it no longer
270 * receives action events from this button. Action events occur
271 * when a user presses or releases the mouse over this button.
272 * If l is null, no exception is thrown and no action is performed.
273 * <p>Refer to <a href="doc-files/AWTThreadIssues.html#ListenersThreads"
274 * >AWT Threading Issues</a> for details on AWT's threading model.
275 *
276 * @param l the action listener
277 * @see #addActionListener
278 * @see #getActionListeners
279 * @see java.awt.event.ActionListener
280 * @since JDK1.1
281 */
282 public synchronized void removeActionListener(ActionListener l) {
283 if (l == null) {
284 return;
285 }
286 actionListener = AWTEventMulticaster.remove(actionListener, l);
287 }
288
289 /**
290 * Returns an array of all the action listeners
291 * registered on this button.
292 *
293 * @return all of this button's <code>ActionListener</code>s
294 * or an empty array if no action
295 * listeners are currently registered
296 *
297 * @see #addActionListener
298 * @see #removeActionListener
299 * @see java.awt.event.ActionListener
300 * @since 1.4
301 */
302 public synchronized ActionListener[] getActionListeners() {
303 return (ActionListener[]) (getListeners(ActionListener.class));
304 }
305
306 /**
307 * Returns an array of all the objects currently registered
308 * as <code><em>Foo</em>Listener</code>s
309 * upon this <code>Button</code>.
310 * <code><em>Foo</em>Listener</code>s are registered using the
311 * <code>add<em>Foo</em>Listener</code> method.
312 *
313 * <p>
314 * You can specify the <code>listenerType</code> argument
315 * with a class literal, such as
316 * <code><em>Foo</em>Listener.class</code>.
317 * For example, you can query a
318 * <code>Button</code> <code>b</code>
319 * for its action listeners with the following code:
320 *
321 * <pre>ActionListener[] als = (ActionListener[])(b.getListeners(ActionListener.class));</pre>
322 *
323 * If no such listeners exist, this method returns an empty array.
324 *
325 * @param listenerType the type of listeners requested; this parameter
326 * should specify an interface that descends from
327 * <code>java.util.EventListener</code>
328 * @return an array of all objects registered as
329 * <code><em>Foo</em>Listener</code>s on this button,
330 * or an empty array if no such
331 * listeners have been added
332 * @exception ClassCastException if <code>listenerType</code>
333 * doesn't specify a class or interface that implements
334 * <code>java.util.EventListener</code>
335 *
336 * @see #getActionListeners
337 * @since 1.3
338 */
339 public <T extends EventListener> T[] getListeners(Class<T> listenerType) {
340 EventListener l = null;
341 if (listenerType == ActionListener.class) {
342 l = actionListener;
343 } else {
344 return super.getListeners(listenerType);
345 }
346 return AWTEventMulticaster.getListeners(l, listenerType);
347 }
348
349 // REMIND: remove when filtering is done at lower level
350 boolean eventEnabled(AWTEvent e) {
351 if (e.id == ActionEvent.ACTION_PERFORMED) {
352 if ((eventMask & AWTEvent.ACTION_EVENT_MASK) != 0 ||
353 actionListener != null) {
354 return true;
355 }
356 return false;
357 }
358 return super.eventEnabled(e);
359 }
360
361 /**
362 * Processes events on this button. If an event is
363 * an instance of <code>ActionEvent</code>, this method invokes
364 * the <code>processActionEvent</code> method. Otherwise,
365 * it invokes <code>processEvent</code> on the superclass.
366 * <p>Note that if the event parameter is <code>null</code>
367 * the behavior is unspecified and may result in an
368 * exception.
369 *
370 * @param e the event
371 * @see java.awt.event.ActionEvent
372 * @see java.awt.Button#processActionEvent
373 * @since JDK1.1
374 */
375 protected void processEvent(AWTEvent e) {
376 if (e instanceof ActionEvent) {
377 processActionEvent((ActionEvent)e);
378 return;
379 }
380 super.processEvent(e);
381 }
382
383 /**
384 * Processes action events occurring on this button
385 * by dispatching them to any registered
386 * <code>ActionListener</code> objects.
387 * <p>
388 * This method is not called unless action events are
389 * enabled for this button. Action events are enabled
390 * when one of the following occurs:
391 * <p><ul>
392 * <li>An <code>ActionListener</code> object is registered
393 * via <code>addActionListener</code>.
394 * <li>Action events are enabled via <code>enableEvents</code>.
395 * </ul>
396 * <p>Note that if the event parameter is <code>null</code>
397 * the behavior is unspecified and may result in an
398 * exception.
399 *
400 * @param e the action event
401 * @see java.awt.event.ActionListener
402 * @see java.awt.Button#addActionListener
403 * @see java.awt.Component#enableEvents
404 * @since JDK1.1
405 */
406 protected void processActionEvent(ActionEvent e) {
407 ActionListener listener = actionListener;
408 if (listener != null) {
409 listener.actionPerformed(e);
410 }
411 }
412
413 /**
414 * Returns a string representing the state of this <code>Button</code>.
415 * This method is intended to be used only for debugging purposes, and the
416 * content and format of the returned string may vary between
417 * implementations. The returned string may be empty but may not be
418 * <code>null</code>.
419 *
420 * @return the parameter string of this button
421 */
422 protected String paramString() {
423 return super.paramString() + ",label=" + label;
424 }
425
426
427 /* Serialization support.
428 */
429
430 /*
431 * Button Serial Data Version.
432 * @serial
433 */
434 private int buttonSerializedDataVersion = 1;
435
436 /**
437 * Writes default serializable fields to stream. Writes
438 * a list of serializable <code>ActionListeners</code>
439 * as optional data. The non-serializable
440 * <code>ActionListeners</code> are detected and
441 * no attempt is made to serialize them.
442 *
443 * @serialData <code>null</code> terminated sequence of 0 or
444 * more pairs: the pair consists of a <code>String</code>
445 * and an <code>Object</code>; the <code>String</code>
446 * indicates the type of object and is one of the following:
447 * <code>actionListenerK</code> indicating an
448 * <code>ActionListener</code> object
449 *
450 * @param s the <code>ObjectOutputStream</code> to write
451 * @see AWTEventMulticaster#save(ObjectOutputStream, String, EventListener)
452 * @see java.awt.Component#actionListenerK
453 * @see #readObject(ObjectInputStream)
454 */
455 private void writeObject(ObjectOutputStream s)
456 throws IOException
457 {
458 s.defaultWriteObject();
459
460 AWTEventMulticaster.save(s, actionListenerK, actionListener);
461 s.writeObject(null);
462 }
463
464 /**
465 * Reads the <code>ObjectInputStream</code> and if
466 * it isn't <code>null</code> adds a listener to
467 * receive action events fired by the button.
468 * Unrecognized keys or values will be ignored.
469 *
470 * @param s the <code>ObjectInputStream</code> to read
471 * @exception HeadlessException if
472 * <code>GraphicsEnvironment.isHeadless</code> returns
473 * <code>true</code>
474 * @serial
475 * @see #removeActionListener(ActionListener)
476 * @see #addActionListener(ActionListener)
477 * @see java.awt.GraphicsEnvironment#isHeadless
478 * @see #writeObject(ObjectOutputStream)
479 */
480 private void readObject(ObjectInputStream s)
481 throws ClassNotFoundException, IOException, HeadlessException
482 {
483 GraphicsEnvironment.checkHeadless();
484 s.defaultReadObject();
485
486 Object keyOrNull;
487 while(null != (keyOrNull = s.readObject())) {
488 String key = ((String)keyOrNull).intern();
489
490 if (actionListenerK == key)
491 addActionListener((ActionListener)(s.readObject()));
492
493 else // skip value for unrecognized key
494 s.readObject();
495 }
496 }
497
498
499 /////////////////
500 // Accessibility support
501 ////////////////
502
503 /**
504 * Gets the <code>AccessibleContext</code> associated with
505 * this <code>Button</code>. For buttons, the
506 * <code>AccessibleContext</code> takes the form of an
507 * <code>AccessibleAWTButton</code>.
508 * A new <code>AccessibleAWTButton</code> instance is
509 * created if necessary.
510 *
511 * @return an <code>AccessibleAWTButton</code> that serves as the
512 * <code>AccessibleContext</code> of this <code>Button</code>
513 * @beaninfo
514 * expert: true
515 * description: The AccessibleContext associated with this Button.
516 * @since 1.3
517 */
518 public AccessibleContext getAccessibleContext() {
519 if (accessibleContext == null) {
520 accessibleContext = new AccessibleAWTButton();
521 }
522 return accessibleContext;
523 }
524
525 /**
526 * This class implements accessibility support for the
527 * <code>Button</code> class. It provides an implementation of the
528 * Java Accessibility API appropriate to button user-interface elements.
529 * @since 1.3
530 */
531 protected class AccessibleAWTButton extends AccessibleAWTComponent
532 implements AccessibleAction, AccessibleValue
533 {
534 /*
535 * JDK 1.3 serialVersionUID
536 */
537 private static final long serialVersionUID = -5932203980244017102L;
538
539 /**
540 * Get the accessible name of this object.
541 *
542 * @return the localized name of the object -- can be null if this
543 * object does not have a name
544 */
545 public String getAccessibleName() {
546 if (accessibleName != null) {
547 return accessibleName;
548 } else {
549 if (getLabel() == null) {
550 return super.getAccessibleName();
551 } else {
552 return getLabel();
553 }
554 }
555 }
556
557 /**
558 * Get the AccessibleAction associated with this object. In the
559 * implementation of the Java Accessibility API for this class,
560 * return this object, which is responsible for implementing the
561 * AccessibleAction interface on behalf of itself.
562 *
563 * @return this object
564 */
565 public AccessibleAction getAccessibleAction() {
566 return this;
567 }
568
569 /**
570 * Get the AccessibleValue associated with this object. In the
571 * implementation of the Java Accessibility API for this class,
572 * return this object, which is responsible for implementing the
573 * AccessibleValue interface on behalf of itself.
574 *
575 * @return this object
576 */
577 public AccessibleValue getAccessibleValue() {
578 return this;
579 }
580
581 /**
582 * Returns the number of Actions available in this object. The
583 * default behavior of a button is to have one action - toggle
584 * the button.
585 *
586 * @return 1, the number of Actions in this object
587 */
588 public int getAccessibleActionCount() {
589 return 1;
590 }
591
592 /**
593 * Return a description of the specified action of the object.
594 *
595 * @param i zero-based index of the actions
596 */
597 public String getAccessibleActionDescription(int i) {
598 if (i == 0) {
599 // [[[PENDING: WDW -- need to provide a localized string]]]
600 return "click";
601 } else {
602 return null;
603 }
604 }
605
606 /**
607 * Perform the specified Action on the object
608 *
609 * @param i zero-based index of actions
610 * @return true if the the action was performed; else false.
611 */
612 public boolean doAccessibleAction(int i) {
613 if (i == 0) {
614 // Simulate a button click
615 Toolkit.getEventQueue().postEvent(
616 new ActionEvent(Button.this,
617 ActionEvent.ACTION_PERFORMED,
618 Button.this.getActionCommand()));
619 return true;
620 } else {
621 return false;
622 }
623 }
624
625 /**
626 * Get the value of this object as a Number.
627 *
628 * @return An Integer of 0 if this isn't selected or an Integer of 1 if
629 * this is selected.
630 * @see javax.swing.AbstractButton#isSelected()
631 */
632 public Number getCurrentAccessibleValue() {
633 return Integer.valueOf(0);
634 }
635
636 /**
637 * Set the value of this object as a Number.
638 *
639 * @return True if the value was set.
640 */
641 public boolean setCurrentAccessibleValue(Number n) {
642 return false;
643 }
644
645 /**
646 * Get the minimum value of this object as a Number.
647 *
648 * @return An Integer of 0.
649 */
650 public Number getMinimumAccessibleValue() {
651 return Integer.valueOf(0);
652 }
653
654 /**
655 * Get the maximum value of this object as a Number.
656 *
657 * @return An Integer of 0.
658 */
659 public Number getMaximumAccessibleValue() {
660 return Integer.valueOf(0);
661 }
662
663 /**
664 * Get the role of this object.
665 *
666 * @return an instance of AccessibleRole describing the role of the
667 * object
668 * @see AccessibleRole
669 */
670 public AccessibleRole getAccessibleRole() {
671 return AccessibleRole.PUSH_BUTTON;
672 }
673 } // inner class AccessibleAWTButton
674
675 }
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