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 package java.awt;
26
27 import java.awt.peer.LabelPeer;
28 import java.io.IOException;
29 import java.io.ObjectInputStream;
30 import javax.accessibility;
31
32 /**
33 * A <code>Label</code> object is a component for placing text in a
34 * container. A label displays a single line of read-only text.
35 * The text can be changed by the application, but a user cannot edit it
36 * directly.
37 * <p>
38 * For example, the code . . .
39 * <p>
40 * <hr><blockquote><pre>
41 * setLayout(new FlowLayout(FlowLayout.CENTER, 10, 10));
42 * add(new Label("Hi There!"));
43 * add(new Label("Another Label"));
44 * </pre></blockquote><hr>
45 * <p>
46 * produces the following labels:
47 * <p>
48 * <img src="doc-files/Label-1.gif" alt="Two labels: 'Hi There!' and 'Another label'"
49 * ALIGN=center HSPACE=10 VSPACE=7>
50 *
51 * @author Sami Shaio
52 * @since JDK1.0
53 */
54 public class Label extends Component implements Accessible {
55
56 static {
57 /* ensure that the necessary native libraries are loaded */
58 Toolkit.loadLibraries();
59 if (!GraphicsEnvironment.isHeadless()) {
60 initIDs();
61 }
62 }
63
64 /**
65 * Indicates that the label should be left justified.
66 */
67 public static final int LEFT = 0;
68
69 /**
70 * Indicates that the label should be centered.
71 */
72 public static final int CENTER = 1;
73
74 /**
75 * Indicates that the label should be right justified.
76 * @since JDK1.0t.
77 */
78 public static final int RIGHT = 2;
79
80 /**
81 * The text of this label.
82 * This text can be modified by the program
83 * but never by the user.
84 *
85 * @serial
86 * @see #getText()
87 * @see #setText(String)
88 */
89 String text;
90
91 /**
92 * The label's alignment. The default alignment is set
93 * to be left justified.
94 *
95 * @serial
96 * @see #getAlignment()
97 * @see #setAlignment(int)
98 */
99 int alignment = LEFT;
100
101 private static final String base = "label";
102 private static int nameCounter = 0;
103
104 /*
105 * JDK 1.1 serialVersionUID
106 */
107 private static final long serialVersionUID = 3094126758329070636L;
108
109 /**
110 * Constructs an empty label.
111 * The text of the label is the empty string <code>""</code>.
112 * @exception HeadlessException if GraphicsEnvironment.isHeadless()
113 * returns true.
114 * @see java.awt.GraphicsEnvironment#isHeadless
115 */
116 public Label() throws HeadlessException {
117 this("", LEFT);
118 }
119
120 /**
121 * Constructs a new label with the specified string of text,
122 * left justified.
123 * @param text the string that the label presents.
124 * A <code>null</code> value
125 * will be accepted without causing a NullPointerException
126 * to be thrown.
127 * @exception HeadlessException if GraphicsEnvironment.isHeadless()
128 * returns true.
129 * @see java.awt.GraphicsEnvironment#isHeadless
130 */
131 public Label(String text) throws HeadlessException {
132 this(text, LEFT);
133 }
134
135 /**
136 * Constructs a new label that presents the specified string of
137 * text with the specified alignment.
138 * Possible values for <code>alignment</code> are <code>Label.LEFT</code>,
139 * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
140 * @param text the string that the label presents.
141 * A <code>null</code> value
142 * will be accepted without causing a NullPointerException
143 * to be thrown.
144 * @param alignment the alignment value.
145 * @exception HeadlessException if GraphicsEnvironment.isHeadless()
146 * returns true.
147 * @see java.awt.GraphicsEnvironment#isHeadless
148 */
149 public Label(String text, int alignment) throws HeadlessException {
150 GraphicsEnvironment.checkHeadless();
151 this.text = text;
152 setAlignment(alignment);
153 }
154
155 /**
156 * Read a label from an object input stream.
157 * @exception HeadlessException if
158 * <code>GraphicsEnvironment.isHeadless()</code> returns
159 * <code>true</code>
160 * @serial
161 * @since 1.4
162 * @see java.awt.GraphicsEnvironment#isHeadless
163 */
164 private void readObject(ObjectInputStream s)
165 throws ClassNotFoundException, IOException, HeadlessException {
166 GraphicsEnvironment.checkHeadless();
167 s.defaultReadObject();
168 }
169
170 /**
171 * Construct a name for this component. Called by getName() when the
172 * name is <code>null</code>.
173 */
174 String constructComponentName() {
175 synchronized (Label.class) {
176 return base + nameCounter++;
177 }
178 }
179
180 /**
181 * Creates the peer for this label. The peer allows us to
182 * modify the appearance of the label without changing its
183 * functionality.
184 */
185 public void addNotify() {
186 synchronized (getTreeLock()) {
187 if (peer == null)
188 peer = getToolkit().createLabel(this);
189 super.addNotify();
190 }
191 }
192
193 /**
194 * Gets the current alignment of this label. Possible values are
195 * <code>Label.LEFT</code>, <code>Label.RIGHT</code>, and
196 * <code>Label.CENTER</code>.
197 * @see java.awt.Label#setAlignment
198 */
199 public int getAlignment() {
200 return alignment;
201 }
202
203 /**
204 * Sets the alignment for this label to the specified alignment.
205 * Possible values are <code>Label.LEFT</code>,
206 * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
207 * @param alignment the alignment to be set.
208 * @exception IllegalArgumentException if an improper value for
209 * <code>alignment</code> is given.
210 * @see java.awt.Label#getAlignment
211 */
212 public synchronized void setAlignment(int alignment) {
213 switch (alignment) {
214 case LEFT:
215 case CENTER:
216 case RIGHT:
217 this.alignment = alignment;
218 LabelPeer peer = (LabelPeer)this.peer;
219 if (peer != null) {
220 peer.setAlignment(alignment);
221 }
222 return;
223 }
224 throw new IllegalArgumentException("improper alignment: " + alignment);
225 }
226
227 /**
228 * Gets the text of this label.
229 * @return the text of this label, or <code>null</code> if
230 * the text has been set to <code>null</code>.
231 * @see java.awt.Label#setText
232 */
233 public String getText() {
234 return text;
235 }
236
237 /**
238 * Sets the text for this label to the specified text.
239 * @param text the text that this label displays. If
240 * <code>text</code> is <code>null</code>, it is
241 * treated for display purposes like an empty
242 * string <code>""</code>.
243 * @see java.awt.Label#getText
244 */
245 public void setText(String text) {
246 boolean testvalid = false;
247 synchronized (this) {
248 if (text != this.text && (this.text == null ||
249 !this.text.equals(text))) {
250 this.text = text;
251 LabelPeer peer = (LabelPeer)this.peer;
252 if (peer != null) {
253 peer.setText(text);
254 }
255 testvalid = true;
256 }
257 }
258
259 // This could change the preferred size of the Component.
260 if (testvalid && valid) {
261 invalidate();
262 }
263 }
264
265 /**
266 * Returns a string representing the state of this <code>Label</code>.
267 * This method is intended to be used only for debugging purposes, and the
268 * content and format of the returned string may vary between
269 * implementations. The returned string may be empty but may not be
270 * <code>null</code>.
271 *
272 * @return the parameter string of this label
273 */
274 protected String paramString() {
275 String str = ",align=";
276 switch (alignment) {
277 case LEFT: str += "left"; break;
278 case CENTER: str += "center"; break;
279 case RIGHT: str += "right"; break;
280 }
281 return super.paramString() + str + ",text=" + text;
282 }
283
284 /**
285 * Initialize JNI field and method IDs
286 */
287 private static native void initIDs();
288
289
290 /////////////////
291 // Accessibility support
292 ////////////////
293
294
295 /**
296 * Gets the AccessibleContext associated with this Label.
297 * For labels, the AccessibleContext takes the form of an
298 * AccessibleAWTLabel.
299 * A new AccessibleAWTLabel instance is created if necessary.
300 *
301 * @return an AccessibleAWTLabel that serves as the
302 * AccessibleContext of this Label
303 * @since 1.3
304 */
305 public AccessibleContext getAccessibleContext() {
306 if (accessibleContext == null) {
307 accessibleContext = new AccessibleAWTLabel();
308 }
309 return accessibleContext;
310 }
311
312 /**
313 * This class implements accessibility support for the
314 * <code>Label</code> class. It provides an implementation of the
315 * Java Accessibility API appropriate to label user-interface elements.
316 * @since 1.3
317 */
318 protected class AccessibleAWTLabel extends AccessibleAWTComponent
319 {
320 /*
321 * JDK 1.3 serialVersionUID
322 */
323 private static final long serialVersionUID = -3568967560160480438L;
324
325 public AccessibleAWTLabel() {
326 super();
327 }
328
329 /**
330 * Get the accessible name of this object.
331 *
332 * @return the localized name of the object -- can be null if this
333 * object does not have a name
334 * @see AccessibleContext#setAccessibleName
335 */
336 public String getAccessibleName() {
337 if (accessibleName != null) {
338 return accessibleName;
339 } else {
340 if (getText() == null) {
341 return super.getAccessibleName();
342 } else {
343 return getText();
344 }
345 }
346 }
347
348 /**
349 * Get the role of this object.
350 *
351 * @return an instance of AccessibleRole describing the role of the object
352 * @see AccessibleRole
353 */
354 public AccessibleRole getAccessibleRole() {
355 return AccessibleRole.LABEL;
356 }
357
358 } // inner class AccessibleAWTLabel
359
360 }
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