001    /* Panel.java -- Simple container object
002       Copyright (C) 1999, 2002, 2004, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.awt;
040    
041    import javax.accessibility.Accessible;
042    import javax.accessibility.AccessibleContext;
043    import javax.accessibility.AccessibleRole;
044    
045    /**
046     * A panel is a simple container class. It's default layout is the
047     * <code>FlowLayout</code> manager.
048     *
049     * @author Aaron M. Renn (arenn@urbanophile.com)
050     * @author Eric Blake (ebb9@email.byu.edu)
051     * @see FlowLayout
052     * @since 1.0
053     * @status updated to 1.4
054     */
055    public class Panel extends Container implements Accessible
056    {
057      /**
058       * Compatible with JDK 1.0+.
059       */
060      private static final long serialVersionUID = -2728009084054400034L;
061    
062      /** The cached accessible context. */
063      private transient AccessibleContext context;
064    
065      /** Flag set when the first system-requested paint event is
066          dispatched. */
067      private transient boolean initialSystemUpdateDone;
068    
069      /** Flag set when the first application-requested paint event is
070          consumed. */
071      private transient boolean initialUpdateConsumed;
072    
073      /*
074       * The number used to generate the name returned by getName.
075       */
076      private static transient long next_panel_number;
077    
078      /**
079       * Initializes a new instance of <code>Panel</code> that has a default
080       * layout manager of <code>FlowLayout</code>.
081       */
082      public Panel()
083      {
084        this(new FlowLayout());
085      }
086    
087      /**
088       * Initializes a new instance of <code>Panel</code> with the specified
089       * layout manager.
090       *
091       * @param layoutManager the layout manager for this object
092       * @since 1.1
093       */
094      public Panel(LayoutManager layoutManager)
095      {
096        setLayout(layoutManager);
097      }
098    
099      /**
100       * Notifies this object to create its native peer.
101       *
102       * @see #isDisplayable()
103       * @see #removeNotify()
104       */
105      public void addNotify()
106      {
107        if (peer == null)
108          peer = getToolkit().createPanel(this);
109        super.addNotify();
110      }
111    
112      /**
113       * Gets the AccessibleContext associated with this panel, creating one if
114       * necessary. This always returns an instance of {@link AccessibleAWTPanel}.
115       *
116       * @return the accessibility context of this panel
117       * @since 1.3
118       */
119      public AccessibleContext getAccessibleContext()
120      {
121        if (context == null)
122          context = new AccessibleAWTPanel();
123        return context;
124      }
125    
126      /**
127       * This class provides accessibility support for Panels, and is the
128       * runtime type returned by {@link #getAccessibleContext()}.
129       *
130       * @author Eric Blake (ebb9@email.byu.edu)
131       * @since 1.3
132       */
133      protected class AccessibleAWTPanel extends AccessibleAWTContainer
134      {
135        /**
136         * Compatible with JDK 1.4+.
137         */
138        private static final long serialVersionUID = -6409552226660031050L;
139    
140        /**
141         * The default constructor.
142         */
143        protected AccessibleAWTPanel()
144        {
145        }
146    
147        /**
148         * Get the role of this accessible object, a panel.
149         *
150         * @return the role of the object
151         * @see AccessibleRole#PANEL
152         */
153        public AccessibleRole getAccessibleRole()
154        {
155          return AccessibleRole.PANEL;
156        }
157      }
158    
159      /**
160       * Generate a unique name for this panel.
161       *
162       * @return A unique name for this panel.
163       */
164      String generateName ()
165      {
166        return "panel" + getUniqueLong ();
167      }
168    
169      private static synchronized long getUniqueLong ()
170      {
171        return next_panel_number++;
172      }
173    }