001    /* DefaultFocusTraversalPolicy.java -- 
002       Copyright (C) 2002, 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    /**
042     * DefaultFocusTraversalPolicy is the default focus traversal policy
043     * used by Containers.
044     *
045     * This policy sharpens ContainerOrderFocusTraversalPolicy's
046     * acceptance criteria, to reject those Components that have
047     * unfocusable peers.  Despite this extra strictness, this policy will
048     * always accept a Component that has explicitly been set focusable by
049     * any means.
050     *
051     * This AWT implementation assumes that the peers of the following
052     * Components are not focusable: Canvas, Panel, Label, ScrollPane,
053     * Scrollbar, Window, and any lightweight Component.
054     *
055     * A Component's focusability is independent of the focusability of
056     * its peer.
057     *
058     * @author Thomas Fitzsimmons (fitzsim@redhat.com)
059     * @since 1.4
060     */
061    public class DefaultFocusTraversalPolicy
062      extends ContainerOrderFocusTraversalPolicy
063    {
064      private static final long serialVersionUID = 8876966522510157497L;
065    
066      /**
067       * Construct a default focus traversal policy.
068       */
069      public DefaultFocusTraversalPolicy ()
070      {
071      }
072    
073      /**
074       * Check whether a given Component would be acceptable as a focus
075       * owner.  The Component must be displayable, visible and enabled to
076       * be acceptable.  If the Component's focus traversability has been
077       * overridden, by overriding Component.isFocusTraversable or
078       * Component.isFocusable, or by calling Component.setFocusable, then
079       * the Component will be accepted if it is focusable.  If the
080       * Component uses the default focus traversable behaviour, then
081       * <code>comp</code> will always be rejected if it is a Canvas,
082       * Panel, Label, ScrollPane, Scrollbar, Window or lightweight
083       * Component.
084       *
085       * @param comp the Component to check
086       *
087       * @return true if the Component is an acceptable target for
088       * keyboard input focus, false otherwise
089       */
090      protected boolean accept (Component comp)
091      {
092        if (comp.visible
093            && comp.isDisplayable ()
094            && comp.enabled)
095          {
096            if (comp.isFocusTraversableOverridden != 0
097                && (comp.isFocusTraversable () || comp.isFocusable()))
098              return true;
099            
100            if (!(comp instanceof Canvas
101                  || comp instanceof Panel
102                  || comp instanceof Label
103                  || comp instanceof ScrollPane
104                  || comp instanceof Scrollbar
105                  || comp instanceof Window
106                  || comp.isLightweight ()))
107              return true;
108          }
109        return false;
110      }
111    }