001 /* Label.java -- Java label widget
002 Copyright (C) 1999, 2000, 2002, 2004, 2005, 2006, Free Software
003 Foundation, Inc.
004
005 This file is part of GNU Classpath.
006
007 GNU Classpath is free software; you can redistribute it and/or modify
008 it under the terms of the GNU General Public License as published by
009 the Free Software Foundation; either version 2, or (at your option)
010 any later version.
011
012 GNU Classpath is distributed in the hope that it will be useful, but
013 WITHOUT ANY WARRANTY; without even the implied warranty of
014 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015 General Public License for more details.
016
017 You should have received a copy of the GNU General Public License
018 along with GNU Classpath; see the file COPYING. If not, write to the
019 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020 02110-1301 USA.
021
022 Linking this library statically or dynamically with other modules is
023 making a combined work based on this library. Thus, the terms and
024 conditions of the GNU General Public License cover the whole
025 combination.
026
027 As a special exception, the copyright holders of this library give you
028 permission to link this library with independent modules to produce an
029 executable, regardless of the license terms of these independent
030 modules, and to copy and distribute the resulting executable under
031 terms of your choice, provided that you also meet, for each linked
032 independent module, the terms and conditions of the license of that
033 module. An independent module is a module which is not derived from
034 or based on this library. If you modify this library, you may extend
035 this exception to your version of the library, but you are not
036 obligated to do so. If you do not wish to do so, delete this
037 exception statement from your version. */
038
039
040 package java.awt;
041
042 import java.awt.peer.LabelPeer;
043
044 import javax.accessibility.Accessible;
045 import javax.accessibility.AccessibleContext;
046 import javax.accessibility.AccessibleRole;
047
048 /**
049 * This component is used for displaying simple text strings that cannot
050 * be edited by the user.
051 *
052 * @author Aaron M. Renn (arenn@urbanophile.com)
053 * @author Tom Tromey (tromey@cygnus.com)
054 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
055 */
056 public class Label extends Component implements Accessible
057 {
058
059 /**
060 * Alignment constant aligning the text to the left of its window.
061 */
062 public static final int LEFT = 0;
063
064 /**
065 * Alignment constant aligning the text in the center of its window.
066 */
067 public static final int CENTER = 1;
068
069 /**
070 * Alignment constant aligning the text to the right of its window.
071 */
072 public static final int RIGHT = 2;
073
074 // Serialization version constant:
075 private static final long serialVersionUID = 3094126758329070636L;
076
077 /**
078 * @serial Indicates the alignment of the text within this label's window.
079 * This is one of the constants in this class. The default value is
080 * <code>LEFT</code>.
081 */
082 private int alignment;
083
084 /**
085 * @serial The text displayed in the label
086 */
087 private String text;
088
089 /**
090 * Initializes a new instance of <code>Label</code> with no text.
091 *
092 * @exception HeadlessException If GraphicsEnvironment.isHeadless() is true.
093 */
094 public Label()
095 {
096 this("", LEFT);
097 }
098
099 /**
100 * Initializes a new instance of <code>Label</code> with the specified
101 * text that is aligned to the left.
102 *
103 * @param text The text of the label.
104 *
105 * @exception HeadlessException If GraphicsEnvironment.isHeadless() is true.
106 */
107 public Label(String text)
108 {
109 this(text, LEFT);
110 }
111
112 /**
113 * Initializes a new instance of <code>Label</code> with the specified
114 * text and alignment.
115 *
116 * @param text The text of the label.
117 * @param alignment The desired alignment for the text in this label,
118 * which must be one of <code>LEFT</code>, <code>CENTER</code>, or
119 * <code>RIGHT</code>.
120 *
121 * @exception HeadlessException If GraphicsEnvironment.isHeadless() is true.
122 */
123 public Label(String text, int alignment)
124 {
125 setAlignment(alignment);
126 setText(text);
127
128 if (GraphicsEnvironment.isHeadless())
129 throw new HeadlessException();
130 }
131
132 /**
133 * Returns the constant indicating the alignment of the text in this
134 * label. The value returned will be one of the alignment constants
135 * from this class.
136 *
137 * @return The alignment of the text in the label.
138 */
139 public int getAlignment()
140 {
141 return(alignment);
142 }
143
144 /**
145 * Sets the text alignment of this label to the specified value.
146 *
147 * @param alignment The desired alignment for the text in this label,
148 * which must be one of <code>LEFT</code>, <code>CENTER</code>, or
149 * <code>RIGHT</code>.
150 */
151 public synchronized void setAlignment(int alignment)
152 {
153 if (alignment != CENTER && alignment != LEFT && alignment != RIGHT)
154 throw new IllegalArgumentException("invalid alignment: " + alignment);
155 this.alignment = alignment;
156 if (peer != null)
157 {
158 LabelPeer lp = (LabelPeer) peer;
159 lp.setAlignment(alignment);
160 }
161 }
162
163 /**
164 * Returns the text displayed in this label.
165 *
166 * @return The text for this label.
167 */
168 public String getText()
169 {
170 return text;
171 }
172
173 /**
174 * Sets the text in this label to the specified value.
175 *
176 * @param text The new text for this label.
177 */
178 public synchronized void setText(String text)
179 {
180 if ((this.text == null && text != null)
181 || (this.text != null && ! this.text.equals(text)))
182 {
183 this.text = text;
184
185 if (peer != null)
186 {
187 LabelPeer lp = (LabelPeer) peer;
188 lp.setText(text);
189 }
190 invalidate();
191 }
192 }
193
194 /**
195 * Notifies this label that it has been added to a container, causing
196 * the peer to be created. This method is called internally by the AWT
197 * system.
198 */
199 public void addNotify()
200 {
201 if (peer == null)
202 peer = getToolkit().createLabel(this);
203 super.addNotify();
204 }
205
206 /**
207 * Returns a parameter string useful for debugging.
208 *
209 * @return A debugging string.
210 */
211 protected String paramString()
212 {
213 return ("text=" + getText() + ",alignment=" +
214 getAlignment() + "," + super.paramString());
215 }
216
217 /**
218 * This class provides accessibility support for the label.
219 */
220 protected class AccessibleAWTLabel
221 extends AccessibleAWTComponent
222 {
223 /**
224 * For compatability with Sun's JDK 1.4.2 rev. 5
225 */
226 private static final long serialVersionUID = -3568967560160480438L;
227
228 /**
229 * Constructor for the accessible label.
230 */
231 public AccessibleAWTLabel()
232 {
233 }
234
235 /**
236 * Returns the accessible name for the label. This is
237 * the text used in the label.
238 *
239 * @return a <code>String</code> containing the accessible
240 * name for this label.
241 */
242 public String getAccessibleName()
243 {
244 return getText();
245 }
246
247 /**
248 * Returns the accessible role for the label.
249 *
250 * @return an instance of <code>AccessibleRole</code>, describing
251 * the role of the label.
252 */
253 public AccessibleRole getAccessibleRole()
254 {
255 return AccessibleRole.LABEL;
256 }
257
258 }
259
260 /**
261 * Gets the AccessibleContext associated with this <code>Label</code>.
262 * The context is created, if necessary.
263 *
264 * @return the associated context
265 */
266 public AccessibleContext getAccessibleContext()
267 {
268 /* Create the context if this is the first request */
269 if (accessibleContext == null)
270 accessibleContext = new AccessibleAWTLabel();
271 return accessibleContext;
272 }
273
274 /**
275 * Generate a unique name for this button.
276 *
277 * @return A unique name for this button.
278 */
279 String generateName()
280 {
281 return "label" + getUniqueLong();
282 }
283
284 /**
285 * The number used to generate the name returned by getName.
286 */
287 private static transient long nextLabelNumber;
288
289 private static synchronized long getUniqueLong()
290 {
291 return nextLabelNumber++;
292 }
293
294 }