libjava/java/awt/Panel.java

   1 /* Panel.java -- Simple container object
   2    Copyright (C) 1999, 2002, 2004, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.awt;
  40
  41 import javax.accessibility.Accessible;
  42 import javax.accessibility.AccessibleContext;
  43 import javax.accessibility.AccessibleRole;
  44
  45 /**
  46  * A panel is a simple container class. It's default layout is the
  47  * <code>FlowLayout</code> manager.
  48  *
  49  * @author Aaron M. Renn (arenn@urbanophile.com)
  50  * @author Eric Blake (ebb9@email.byu.edu)
  51  * @see FlowLayout
  52  * @since 1.0
  53  * @status updated to 1.4
  54  */
  55 public class Panel extends Container implements Accessible
  56 {
  57   /**
  58    * Compatible with JDK 1.0+.
  59    */
  60   private static final long serialVersionUID = -2728009084054400034L;
  61
  62   /** The cached accessible context. */
  63   private transient AccessibleContext context;
  64
  65   /** Flag set when the first system-requested paint event is
  66       dispatched. */
  67   private transient boolean initialSystemUpdateDone;
  68
  69   /** Flag set when the first application-requested paint event is
  70       consumed. */
  71   private transient boolean initialUpdateConsumed;
  72
  73   /*
  74    * The number used to generate the name returned by getName.
  75    */
  76   private static transient long next_panel_number;
  77
  78   /**
  79    * Initializes a new instance of <code>Panel</code> that has a default
  80    * layout manager of <code>FlowLayout</code>.
  81    */
  82   public Panel()
  83   {
  84     this(new FlowLayout());
  85   }
  86
  87   /**
  88    * Initializes a new instance of <code>Panel</code> with the specified
  89    * layout manager.
  90    *
  91    * @param layoutManager the layout manager for this object
  92    * @since 1.1
  93    */
  94   public Panel(LayoutManager layoutManager)
  95   {
  96     setLayout(layoutManager);
  97   }
  98
  99   /**
 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 }