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
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7 * published by the Free Software Foundation. Oracle designates this
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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
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25 package java.awt;
26
27 /**
28 * A FocusTraversalPolicy defines the order in which Components with a
29 * particular focus cycle root are traversed. Instances can apply the policy to
30 * arbitrary focus cycle roots, allowing themselves to be shared across
31 * Containers. They do not need to be reinitialized when the focus cycle roots
32 * of a Component hierarchy change.
33 * <p>
34 * The core responsibility of a FocusTraversalPolicy is to provide algorithms
35 * determining the next and previous Components to focus when traversing
36 * forward or backward in a UI. Each FocusTraversalPolicy must also provide
37 * algorithms for determining the first, last, and default Components in a
38 * traversal cycle. First and last Components are used when normal forward and
39 * backward traversal, respectively, wraps. The default Component is the first
40 * to receive focus when traversing down into a new focus traversal cycle.
41 * A FocusTraversalPolicy can optionally provide an algorithm for determining
42 * a Window's initial Component. The initial Component is the first to receive
43 * focus when a Window is first made visible.
44 * <p>
45 * FocusTraversalPolicy takes into account <a
46 * href="doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus traversal
47 * policy providers</a>. When searching for first/last/next/previous Component,
48 * if a focus traversal policy provider is encountered, its focus traversal
49 * policy is used to perform the search operation.
50 * <p>
51 * Please see
52 * <a href="https://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html">
53 * How to Use the Focus Subsystem</a>,
54 * a section in <em>The Java Tutorial</em>, and the
55 * <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>
56 * for more information.
57 *
58 * @author David Mendenhall
59 *
60 * @see Container#setFocusTraversalPolicy
61 * @see Container#getFocusTraversalPolicy
62 * @see Container#setFocusCycleRoot
63 * @see Container#isFocusCycleRoot
64 * @see Container#setFocusTraversalPolicyProvider
65 * @see Container#isFocusTraversalPolicyProvider
66 * @see KeyboardFocusManager#setDefaultFocusTraversalPolicy
67 * @see KeyboardFocusManager#getDefaultFocusTraversalPolicy
68 * @since 1.4
69 */
70 public abstract class FocusTraversalPolicy {
71
72 /**
73 * Returns the Component that should receive the focus after aComponent.
74 * aContainer must be a focus cycle root of aComponent or a focus traversal
75 * policy provider.
76 *
77 * @param aContainer a focus cycle root of aComponent or focus traversal
78 * policy provider
79 * @param aComponent a (possibly indirect) child of aContainer, or
80 * aContainer itself
81 * @return the Component that should receive the focus after aComponent, or
82 * null if no suitable Component can be found
83 * @throws IllegalArgumentException if aContainer is not a focus cycle
84 * root of aComponent or a focus traversal policy provider, or if
85 * either aContainer or aComponent is null
86 */
87 public abstract Component getComponentAfter(Container aContainer,
88 Component aComponent);
89
90 /**
91 * Returns the Component that should receive the focus before aComponent.
92 * aContainer must be a focus cycle root of aComponent or a focus traversal
93 * policy provider.
94 *
95 * @param aContainer a focus cycle root of aComponent or focus traversal
96 * policy provider
97 * @param aComponent a (possibly indirect) child of aContainer, or
98 * aContainer itself
99 * @return the Component that should receive the focus before aComponent,
100 * or null if no suitable Component can be found
101 * @throws IllegalArgumentException if aContainer is not a focus cycle
102 * root of aComponent or a focus traversal policy provider, or if
103 * either aContainer or aComponent is null
104 */
105 public abstract Component getComponentBefore(Container aContainer,
106 Component aComponent);
107
108 /**
109 * Returns the first Component in the traversal cycle. This method is used
110 * to determine the next Component to focus when traversal wraps in the
111 * forward direction.
112 *
113 * @param aContainer the focus cycle root or focus traversal policy provider
114 * whose first Component is to be returned
115 * @return the first Component in the traversal cycle of aContainer,
116 * or null if no suitable Component can be found
117 * @throws IllegalArgumentException if aContainer is null
118 */
119 public abstract Component getFirstComponent(Container aContainer);
120
121 /**
122 * Returns the last Component in the traversal cycle. This method is used
123 * to determine the next Component to focus when traversal wraps in the
124 * reverse direction.
125 *
126 * @param aContainer the focus cycle root or focus traversal policy
127 * provider whose last Component is to be returned
128 * @return the last Component in the traversal cycle of aContainer,
129 * or null if no suitable Component can be found
130 * @throws IllegalArgumentException if aContainer is null
131 */
132 public abstract Component getLastComponent(Container aContainer);
133
134 /**
135 * Returns the default Component to focus. This Component will be the first
136 * to receive focus when traversing down into a new focus traversal cycle
137 * rooted at aContainer.
138 *
139 * @param aContainer the focus cycle root or focus traversal policy
140 * provider whose default Component is to be returned
141 * @return the default Component in the traversal cycle of aContainer,
142 * or null if no suitable Component can be found
143 * @throws IllegalArgumentException if aContainer is null
144 */
145 public abstract Component getDefaultComponent(Container aContainer);
146
147 /**
148 * Returns the Component that should receive the focus when a Window is
149 * made visible for the first time. Once the Window has been made visible
150 * by a call to <code>show()</code> or <code>setVisible(true)</code>, the
151 * initial Component will not be used again. Instead, if the Window loses
152 * and subsequently regains focus, or is made invisible or undisplayable
153 * and subsequently made visible and displayable, the Window's most
154 * recently focused Component will become the focus owner. The default
155 * implementation of this method returns the default Component.
156 *
157 * @param window the Window whose initial Component is to be returned
158 * @return the Component that should receive the focus when window is made
159 * visible for the first time, or null if no suitable Component can
160 * be found
161 * @see #getDefaultComponent
162 * @see Window#getMostRecentFocusOwner
163 * @throws IllegalArgumentException if window is null
164 */
165 public Component getInitialComponent(Window window) {
166 if ( window == null ){
167 throw new IllegalArgumentException("window cannot be equal to null.");
168 }
169 Component def = getDefaultComponent(window);
170 if (def == null && window.isFocusableWindow()) {
171 def = window;
172 }
173 return def;
174 }
175 }