1 /*
2 * Copyright (c) 1996, 2015, Oracle and/or its affiliates. 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.awt.event;
27
28 import sun.awt.AppContext;
29 import sun.awt.SunToolkit;
30
31 import java.awt.*;
32
33 /**
34 * A low-level event which indicates that a Component has gained or lost the
35 * input focus. This low-level event is generated by a Component (such as a
36 * TextField). The event is passed to every {@code FocusListener} or
37 * {@code FocusAdapter} object which registered to receive such events
38 * using the Component's {@code addFocusListener} method. ({@code
39 * FocusAdapter} objects implement the {@code FocusListener}
40 * interface.) Each such listener object gets this {@code FocusEvent} when
41 * the event occurs.
42 * <p>
43 * There are two levels of focus events: permanent and temporary. Permanent
44 * focus change events occur when focus is directly moved from one Component to
45 * another, such as through a call to requestFocus() or as the user uses the
46 * TAB key to traverse Components. Temporary focus change events occur when
47 * focus is temporarily lost for a Component as the indirect result of another
48 * operation, such as Window deactivation or a Scrollbar drag. In this case,
49 * the original focus state will automatically be restored once that operation
50 * is finished, or, for the case of Window deactivation, when the Window is
51 * reactivated. Both permanent and temporary focus events are delivered using
52 * the FOCUS_GAINED and FOCUS_LOST event ids; the level may be distinguished in
53 * the event using the isTemporary() method.
54 * <p>
55 * Every {@code FocusEvent} records its cause - the reason why this event was
56 * generated. The cause is assigned during the focus event creation and may be
57 * retrieved by calling {@link #getCause}.
58 * <p>
59 * An unspecified behavior will be caused if the {@code id} parameter
60 * of any particular {@code FocusEvent} instance is not
61 * in the range from {@code FOCUS_FIRST} to {@code FOCUS_LAST}.
62 *
63 * @see FocusAdapter
64 * @see FocusListener
65 * @see <a href="http://docs.oracle.com/javase/tutorial/uiswing/events/focuslistener.html">Tutorial: Writing a Focus Listener</a>
66 *
67 * @author Carl Quinn
68 * @author Amy Fowler
69 * @since 1.1
70 */
71 public class FocusEvent extends ComponentEvent {
72
73 /**
74 * This enum represents the cause of a {@code FocusEvent}- the reason why it
75 * occurred. Possible reasons include mouse events, keyboard focus
76 * traversal, window activation.
77 * If no cause is provided then the reason is {@code UNKNOWN}.
78 *
79 * @since 1.9
80 */
81 public enum Cause {
82 /**
83 * The default value.
84 */
85 UNKNOWN,
86 /**
87 * An activating mouse event.
88 */
89 MOUSE_EVENT,
90 /**
91 * A focus traversal action with unspecified direction.
92 */
93 TRAVERSAL,
94 /**
95 * An up-cycle focus traversal action.
96 */
97 TRAVERSAL_UP,
98 /**
99 * A down-cycle focus traversal action.
100 */
101 TRAVERSAL_DOWN,
102 /**
103 * A forward focus traversal action.
104 */
105 TRAVERSAL_FORWARD,
106 /**
107 * A backward focus traversal action.
108 */
109 TRAVERSAL_BACKWARD,
110 /**
111 * Restoring focus after a focus request has been rejected.
112 */
113 ROLLBACK,
114 /**
115 * A system action causing an unexpected focus change.
116 */
117 UNEXPECTED,
118 /**
119 * An activation of a toplevel window.
120 */
121 ACTIVATION,
122 /**
123 * Clearing global focus owner.
124 */
125 CLEAR_GLOBAL_FOCUS_OWNER
126 }
127
128 /**
129 * The first number in the range of ids used for focus events.
130 */
131 public static final int FOCUS_FIRST = 1004;
132
133 /**
134 * The last number in the range of ids used for focus events.
135 */
136 public static final int FOCUS_LAST = 1005;
137
138 /**
139 * This event indicates that the Component is now the focus owner.
140 */
141 public static final int FOCUS_GAINED = FOCUS_FIRST; //Event.GOT_FOCUS
142
143 /**
144 * This event indicates that the Component is no longer the focus owner.
145 */
146 public static final int FOCUS_LOST = 1 + FOCUS_FIRST; //Event.LOST_FOCUS
147
148 private final Cause cause;
149
150 /**
151 * A focus event can have two different levels, permanent and temporary.
152 * It will be set to true if some operation takes away the focus
153 * temporarily and intends on getting it back once the event is completed.
154 * Otherwise it will be set to false.
155 *
156 * @serial
157 * @see #isTemporary
158 */
159 boolean temporary;
160
161 /**
162 * The other Component involved in this focus change. For a FOCUS_GAINED
163 * event, this is the Component that lost focus. For a FOCUS_LOST event,
164 * this is the Component that gained focus. If this focus change occurs
165 * with a native application, a Java application in a different VM, or with
166 * no other Component, then the opposite Component is null.
167 *
168 * @see #getOppositeComponent
169 * @since 1.4
170 */
171 transient Component opposite;
172
173 /*
174 * JDK 1.9 serialVersionUID
175 */
176 private static final long serialVersionUID = 523753786457416397L;
177
178 /**
179 * Constructs a {@code FocusEvent} object with the
180 * specified temporary state and opposite {@code Component} and the
181 * {@code Cause.UNKNOWN} cause.
182 * The opposite {@code Component} is the other
183 * {@code Component} involved in this focus change.
184 * For a {@code FOCUS_GAINED} event, this is the
185 * {@code Component} that lost focus. For a
186 * {@code FOCUS_LOST} event, this is the {@code Component}
187 * that gained focus. If this focus change occurs with a native
188 * application, with a Java application in a different VM,
189 * or with no other {@code Component}, then the opposite
190 * {@code Component} is {@code null}.
191 * <p> This method throws an
192 * {@code IllegalArgumentException} if {@code source}
193 * is {@code null}.
194 *
195 * @param source The {@code Component} that originated the event
196 * @param id An integer indicating the type of event.
197 * For information on allowable values, see
198 * the class description for {@link FocusEvent}
199 * @param temporary Equals {@code true} if the focus change is temporary;
200 * {@code false} otherwise
201 * @param opposite The other Component involved in the focus change,
202 * or {@code null}
203 * @throws IllegalArgumentException if {@code source} equals {@code null}
204 * @see #getSource()
205 * @see #getID()
206 * @see #isTemporary()
207 * @see #getOppositeComponent()
208 * @see Cause#UNKNOWN
209 * @since 1.4
210 */
211 public FocusEvent(Component source, int id, boolean temporary,
212 Component opposite) {
213 this(source, id, temporary, opposite, Cause.UNKNOWN);
214 }
215
216 /**
217 * Constructs a {@code FocusEvent} object with the
218 * specified temporary state, opposite {@code Component} and the cause.
219 * The opposite {@code Component} is the other
220 * {@code Component} involved in this focus change.
221 * For a {@code FOCUS_GAINED} event, this is the
222 * {@code Component} that lost focus. For a
223 * {@code FOCUS_LOST} event, this is the {@code Component}
224 * that gained focus. If this focus change occurs with a native
225 * application, with a Java application in a different VM,
226 * or with no other {@code Component}, then the opposite
227 * {@code Component} is {@code null}.
228 * <p> This method throws an
229 * {@code IllegalArgumentException} if {@code source}
230 * is {@code null}.
231 *
232 * @param source The {@code Component} that originated the event
233 * @param id An integer indicating the type of event.
234 * For information on allowable values, see
235 * the class description for {@link FocusEvent}
236 * @param temporary Equals {@code true} if the focus change is temporary;
237 * {@code false} otherwise
238 * @param opposite The other Component involved in the focus change,
239 * or {@code null}
240 * @param cause The focus event cause.
241 * @throws IllegalArgumentException if {@code source} equals {@code null}
242 * or if {@code cause} equals {@code null}
243 * @see #getSource()
244 * @see #getID()
245 * @see #isTemporary()
246 * @see #getOppositeComponent()
247 * @see Cause
248 * @since 1.9
249 */
250 public FocusEvent(Component source, int id, boolean temporary,
251 Component opposite, Cause cause) {
252 super(source, id);
253 if (cause == null) {
254 throw new IllegalArgumentException("null cause");
255 }
256 this.temporary = temporary;
257 this.opposite = opposite;
258 this.cause = cause;
259 }
260
261 /**
262 * Constructs a {@code FocusEvent} object and identifies
263 * whether or not the change is temporary.
264 * <p> This method throws an
265 * {@code IllegalArgumentException} if {@code source}
266 * is {@code null}.
267 *
268 * @param source The {@code Component} that originated the event
269 * @param id An integer indicating the type of event.
270 * For information on allowable values, see
271 * the class description for {@link FocusEvent}
272 * @param temporary Equals {@code true} if the focus change is temporary;
273 * {@code false} otherwise
274 * @throws IllegalArgumentException if {@code source} equals {@code null}
275 * @see #getSource()
276 * @see #getID()
277 * @see #isTemporary()
278 */
279 public FocusEvent(Component source, int id, boolean temporary) {
280 this(source, id, temporary, null);
281 }
282
283 /**
284 * Constructs a {@code FocusEvent} object and identifies it
285 * as a permanent change in focus.
286 * <p> This method throws an
287 * {@code IllegalArgumentException} if {@code source}
288 * is {@code null}.
289 *
290 * @param source The {@code Component} that originated the event
291 * @param id An integer indicating the type of event.
292 * For information on allowable values, see
293 * the class description for {@link FocusEvent}
294 * @throws IllegalArgumentException if {@code source} equals {@code null}
295 * @see #getSource()
296 * @see #getID()
297 */
298 public FocusEvent(Component source, int id) {
299 this(source, id, false);
300 }
301
302 /**
303 * Identifies the focus change event as temporary or permanent.
304 *
305 * @return {@code true} if the focus change is temporary;
306 * {@code false} otherwise
307 */
308 public boolean isTemporary() {
309 return temporary;
310 }
311
312 /**
313 * Returns the other Component involved in this focus change. For a
314 * FOCUS_GAINED event, this is the Component that lost focus. For a
315 * FOCUS_LOST event, this is the Component that gained focus. If this
316 * focus change occurs with a native application, with a Java application
317 * in a different VM or context, or with no other Component, then null is
318 * returned.
319 *
320 * @return the other Component involved in the focus change, or null
321 * @since 1.4
322 */
323 public Component getOppositeComponent() {
324 if (opposite == null) {
325 return null;
326 }
327
328 return (SunToolkit.targetToAppContext(opposite) ==
329 AppContext.getAppContext())
330 ? opposite
331 : null;
332 }
333
334 /**
335 * Returns a parameter string identifying this event.
336 * This method is useful for event-logging and for debugging.
337 *
338 * @return a string identifying the event and its attributes
339 */
340 public String paramString() {
341 String typeStr;
342 switch(id) {
343 case FOCUS_GAINED:
344 typeStr = "FOCUS_GAINED";
345 break;
346 case FOCUS_LOST:
347 typeStr = "FOCUS_LOST";
348 break;
349 default:
350 typeStr = "unknown type";
351 }
352 return typeStr + (temporary ? ",temporary" : ",permanent") +
353 ",opposite=" + getOppositeComponent() + ",cause=" + getCause();
354 }
355
356 /**
357 * Returns the event cause.
358 *
359 * @return one of {@link Cause} values
360 * @since 1.9
361 */
362 public final Cause getCause() {
363 return cause;
364 }
365 }