1 /*
2 * Copyright (c) 1996, 2013, 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 java.awt.Component;
29 import sun.awt.AppContext;
30 import sun.awt.SunToolkit;
31
32 /**
33 * A low-level event which indicates that a Component has gained or lost the
34 * input focus. This low-level event is generated by a Component (such as a
35 * TextField). The event is passed to every <code>FocusListener</code> or
36 * <code>FocusAdapter</code> object which registered to receive such events
37 * using the Component's <code>addFocusListener</code> method. (<code>
38 * FocusAdapter</code> objects implement the <code>FocusListener</code>
39 * interface.) Each such listener object gets this <code>FocusEvent</code> when
40 * the event occurs.
41 * <p>
42 * There are two levels of focus events: permanent and temporary. Permanent
43 * focus change events occur when focus is directly moved from one Component to
44 * another, such as through a call to requestFocus() or as the user uses the
45 * TAB key to traverse Components. Temporary focus change events occur when
46 * focus is temporarily lost for a Component as the indirect result of another
47 * operation, such as Window deactivation or a Scrollbar drag. In this case,
48 * the original focus state will automatically be restored once that operation
49 * is finished, or, for the case of Window deactivation, when the Window is
50 * reactivated. Both permanent and temporary focus events are delivered using
51 * the FOCUS_GAINED and FOCUS_LOST event ids; the level may be distinguished in
52 * the event using the isTemporary() method.
53 * <p>
54 * An unspecified behavior will be caused if the {@code id} parameter
55 * of any particular {@code FocusEvent} instance is not
56 * in the range from {@code FOCUS_FIRST} to {@code FOCUS_LAST}.
57 *
58 * @see FocusAdapter
59 * @see FocusListener
60 * @see <a href="http://docs.oracle.com/javase/tutorial/uiswing/events/focuslistener.html">Tutorial: Writing a Focus Listener</a>
61 *
62 * @author Carl Quinn
63 * @author Amy Fowler
64 * @since 1.1
65 */
66 public class FocusEvent extends ComponentEvent {
67
68 /**
69 * The first number in the range of ids used for focus events.
70 */
71 public static final int FOCUS_FIRST = 1004;
72
73 /**
74 * The last number in the range of ids used for focus events.
75 */
76 public static final int FOCUS_LAST = 1005;
77
78 /**
79 * This event indicates that the Component is now the focus owner.
80 */
81 public static final int FOCUS_GAINED = FOCUS_FIRST; //Event.GOT_FOCUS
82
83 /**
84 * This event indicates that the Component is no longer the focus owner.
85 */
86 public static final int FOCUS_LOST = 1 + FOCUS_FIRST; //Event.LOST_FOCUS
87
88 /**
89 * A focus event can have two different levels, permanent and temporary.
90 * It will be set to true if some operation takes away the focus
91 * temporarily and intends on getting it back once the event is completed.
92 * Otherwise it will be set to false.
93 *
94 * @serial
95 * @see #isTemporary
96 */
97 boolean temporary;
98
99 /**
100 * The other Component involved in this focus change. For a FOCUS_GAINED
101 * event, this is the Component that lost focus. For a FOCUS_LOST event,
102 * this is the Component that gained focus. If this focus change occurs
103 * with a native application, a Java application in a different VM, or with
104 * no other Component, then the opposite Component is null.
105 *
106 * @see #getOppositeComponent
107 * @since 1.4
108 */
109 transient Component opposite;
110
111 /*
112 * JDK 1.1 serialVersionUID
113 */
114 private static final long serialVersionUID = 523753786457416396L;
115
116 /**
117 * Constructs a <code>FocusEvent</code> object with the
118 * specified temporary state and opposite <code>Component</code>.
119 * The opposite <code>Component</code> is the other
120 * <code>Component</code> involved in this focus change.
121 * For a <code>FOCUS_GAINED</code> event, this is the
122 * <code>Component</code> that lost focus. For a
123 * <code>FOCUS_LOST</code> event, this is the <code>Component</code>
124 * that gained focus. If this focus change occurs with a native
125 * application, with a Java application in a different VM,
126 * or with no other <code>Component</code>, then the opposite
127 * <code>Component</code> is <code>null</code>.
128 * <p> This method throws an
129 * <code>IllegalArgumentException</code> if <code>source</code>
130 * is <code>null</code>.
131 *
132 * @param source The <code>Component</code> that originated the event
133 * @param id An integer indicating the type of event.
134 * For information on allowable values, see
135 * the class description for {@link FocusEvent}
136 * @param temporary Equals <code>true</code> if the focus change is temporary;
137 * <code>false</code> otherwise
138 * @param opposite The other Component involved in the focus change,
139 * or <code>null</code>
140 * @throws IllegalArgumentException if <code>source</code> equals {@code null}
141 * @see #getSource()
142 * @see #getID()
143 * @see #isTemporary()
144 * @see #getOppositeComponent()
145 * @since 1.4
146 */
147 public FocusEvent(Component source, int id, boolean temporary,
148 Component opposite) {
149 super(source, id);
150 this.temporary = temporary;
151 this.opposite = opposite;
152 }
153
154 /**
155 * Constructs a <code>FocusEvent</code> object and identifies
156 * whether or not the change is temporary.
157 * <p> This method throws an
158 * <code>IllegalArgumentException</code> if <code>source</code>
159 * is <code>null</code>.
160 *
161 * @param source The <code>Component</code> that originated the event
162 * @param id An integer indicating the type of event.
163 * For information on allowable values, see
164 * the class description for {@link FocusEvent}
165 * @param temporary Equals <code>true</code> if the focus change is temporary;
166 * <code>false</code> otherwise
167 * @throws IllegalArgumentException if <code>source</code> equals {@code null}
168 * @see #getSource()
169 * @see #getID()
170 * @see #isTemporary()
171 */
172 public FocusEvent(Component source, int id, boolean temporary) {
173 this(source, id, temporary, null);
174 }
175
176 /**
177 * Constructs a <code>FocusEvent</code> object and identifies it
178 * as a permanent change in focus.
179 * <p> This method throws an
180 * <code>IllegalArgumentException</code> if <code>source</code>
181 * is <code>null</code>.
182 *
183 * @param source The <code>Component</code> that originated the event
184 * @param id An integer indicating the type of event.
185 * For information on allowable values, see
186 * the class description for {@link FocusEvent}
187 * @throws IllegalArgumentException if <code>source</code> equals {@code null}
188 * @see #getSource()
189 * @see #getID()
190 */
191 public FocusEvent(Component source, int id) {
192 this(source, id, false);
193 }
194
195 /**
196 * Identifies the focus change event as temporary or permanent.
197 *
198 * @return <code>true</code> if the focus change is temporary;
199 * <code>false</code> otherwise
200 */
201 public boolean isTemporary() {
202 return temporary;
203 }
204
205 /**
206 * Returns the other Component involved in this focus change. For a
207 * FOCUS_GAINED event, this is the Component that lost focus. For a
208 * FOCUS_LOST event, this is the Component that gained focus. If this
209 * focus change occurs with a native application, with a Java application
210 * in a different VM or context, or with no other Component, then null is
211 * returned.
212 *
213 * @return the other Component involved in the focus change, or null
214 * @since 1.4
215 */
216 public Component getOppositeComponent() {
217 if (opposite == null) {
218 return null;
219 }
220
221 return (SunToolkit.targetToAppContext(opposite) ==
222 AppContext.getAppContext())
223 ? opposite
224 : null;
225 }
226
227 /**
228 * Returns a parameter string identifying this event.
229 * This method is useful for event-logging and for debugging.
230 *
231 * @return a string identifying the event and its attributes
232 */
233 public String paramString() {
234 String typeStr;
235 switch(id) {
236 case FOCUS_GAINED:
237 typeStr = "FOCUS_GAINED";
238 break;
239 case FOCUS_LOST:
240 typeStr = "FOCUS_LOST";
241 break;
242 default:
243 typeStr = "unknown type";
244 }
245 return typeStr + (temporary ? ",temporary" : ",permanent") +
246 ",opposite=" + getOppositeComponent();
247 }
248
249 }