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    }