1 /*
2 * Copyright (c) 2000, 2015, 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()}. 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()} or
40 * {@code Component.isFocusable()}, or by calling
41 * {@code Component.setFocusable()}, 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="https://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()} or
84 * {@code Component.isFocusable()}, or by calling
85 * {@code Component.setFocusable()}, 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} if aComponent meets the above requirements;
94 * {@code false} 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.peer;
126 return (peer != null && peer.isFocusable());
127 }
128 }
--- EOF ---