View Javadoc
1   /*
2    * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  package java.awt;
26  
27  import java.awt.peer.ComponentPeer;
28  
29  
30  /**
31   * A FocusTraversalPolicy that determines traversal order based on the order
32   * of child Components in a Container. From a particular focus cycle root, the
33   * policy makes a pre-order traversal of the Component hierarchy, and traverses
34   * a Container's children according to the ordering of the array returned by
35   * <code>Container.getComponents()</code>. Portions of the hierarchy that are
36   * not visible and displayable will not be searched.
37   * <p>
38   * If client code has explicitly set the focusability of a Component by either
39   * overriding <code>Component.isFocusTraversable()</code> or
40   * <code>Component.isFocusable()</code>, or by calling
41   * <code>Component.setFocusable()</code>, then a DefaultFocusTraversalPolicy
42   * behaves exactly like a ContainerOrderFocusTraversalPolicy. If, however, the
43   * Component is relying on default focusability, then a
44   * DefaultFocusTraversalPolicy will reject all Components with non-focusable
45   * peers. This is the default FocusTraversalPolicy for all AWT Containers.
46   * <p>
47   * The focusability of a peer is implementation-dependent. Sun recommends that
48   * all implementations for a particular native platform construct peers with
49   * the same focusability. The recommendations for Windows and Unix are that
50   * Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight
51   * Components have non-focusable peers, and all other Components have focusable
52   * peers. These recommendations are used in the Sun AWT implementations. Note
53   * that the focusability of a Component's peer is different from, and does not
54   * impact, the focusability of the Component itself.
55   * <p>
56   * Please see
57   * <a href="http://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html">
58   * How to Use the Focus Subsystem</a>,
59   * a section in <em>The Java Tutorial</em>, and the
60   * <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>
61   * for more information.
62   *
63   * @author David Mendenhall
64   *
65   * @see Container#getComponents
66   * @see Component#isFocusable
67   * @see Component#setFocusable
68   * @since 1.4
69   */
70  public class DefaultFocusTraversalPolicy
71      extends ContainerOrderFocusTraversalPolicy
72  {
73      /*
74       * serialVersionUID
75       */
76      private static final long serialVersionUID = 8876966522510157497L;
77  
78      /**
79       * Determines whether a Component is an acceptable choice as the new
80       * focus owner. The Component must be visible, displayable, and enabled
81       * to be accepted. If client code has explicitly set the focusability
82       * of the Component by either overriding
83       * <code>Component.isFocusTraversable()</code> or
84       * <code>Component.isFocusable()</code>, or by calling
85       * <code>Component.setFocusable()</code>, then the Component will be
86       * accepted if and only if it is focusable. If, however, the Component is
87       * relying on default focusability, then all Canvases, Labels, Panels,
88       * Scrollbars, ScrollPanes, Windows, and lightweight Components will be
89       * rejected.
90       *
91       * @param aComponent the Component whose fitness as a focus owner is to
92       *        be tested
93       * @return <code>true</code> if aComponent meets the above requirements;
94       *         <code>false</code> otherwise
95       */
96      protected boolean accept(Component aComponent) {
97          if (!(aComponent.isVisible() && aComponent.isDisplayable() &&
98                aComponent.isEnabled()))
99          {
100             return false;
101         }
102 
103         // Verify that the Component is recursively enabled. Disabling a
104         // heavyweight Container disables its children, whereas disabling
105         // a lightweight Container does not.
106         if (!(aComponent instanceof Window)) {
107             for (Container enableTest = aComponent.getParent();
108                  enableTest != null;
109                  enableTest = enableTest.getParent())
110             {
111                 if (!(enableTest.isEnabled() || enableTest.isLightweight())) {
112                     return false;
113                 }
114                 if (enableTest instanceof Window) {
115                     break;
116                 }
117             }
118         }
119 
120         boolean focusable = aComponent.isFocusable();
121         if (aComponent.isFocusTraversableOverridden()) {
122             return focusable;
123         }
124 
125         ComponentPeer peer = aComponent.getPeer();
126         return (peer != null && peer.isFocusable());
127     }
128 }