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1 /* |
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2 * Copyright 2000-2004 Sun Microsystems, Inc. All Rights Reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Sun designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Sun in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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22 * CA 95054 USA or visit www.sun.com if you need additional information or |
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23 * have any questions. |
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24 */ |
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25 package java.awt; |
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26 |
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27 import java.awt.peer.ComponentPeer; |
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28 |
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29 |
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30 /** |
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31 * A FocusTraversalPolicy that determines traversal order based on the order |
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32 * of child Components in a Container. From a particular focus cycle root, the |
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33 * policy makes a pre-order traversal of the Component hierarchy, and traverses |
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34 * a Container's children according to the ordering of the array returned by |
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35 * <code>Container.getComponents()</code>. Portions of the hierarchy that are |
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36 * not visible and displayable will not be searched. |
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37 * <p> |
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38 * If client code has explicitly set the focusability of a Component by either |
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39 * overriding <code>Component.isFocusTraversable()</code> or |
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40 * <code>Component.isFocusable()</code>, or by calling |
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41 * <code>Component.setFocusable()</code>, then a DefaultFocusTraversalPolicy |
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42 * behaves exactly like a ContainerOrderFocusTraversalPolicy. If, however, the |
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43 * Component is relying on default focusability, then a |
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44 * DefaultFocusTraversalPolicy will reject all Components with non-focusable |
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45 * peers. This is the default FocusTraversalPolicy for all AWT Containers. |
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46 * <p> |
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47 * The focusability of a peer is implementation-dependent. Sun recommends that |
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48 * all implementations for a particular native platform construct peers with |
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49 * the same focusability. The recommendations for Windows and Unix are that |
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50 * Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight |
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51 * Components have non-focusable peers, and all other Components have focusable |
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52 * peers. These recommendations are used in the Sun AWT implementations. Note |
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53 * that the focusability of a Component's peer is different from, and does not |
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54 * impact, the focusability of the Component itself. |
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55 * <p> |
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56 * Please see |
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57 * <a href="http://java.sun.com/docs/books/tutorial/uiswing/misc/focus.html"> |
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58 * How to Use the Focus Subsystem</a>, |
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59 * a section in <em>The Java Tutorial</em>, and the |
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60 * <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a> |
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61 * for more information. |
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62 * |
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63 * @author David Mendenhall |
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64 * |
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65 * @see Container#getComponents |
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66 * @see Component#isFocusable |
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67 * @see Component#setFocusable |
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68 * @since 1.4 |
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69 */ |
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70 public class DefaultFocusTraversalPolicy |
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71 extends ContainerOrderFocusTraversalPolicy |
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72 { |
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73 /* |
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74 * serialVersionUID |
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75 */ |
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76 private static final long serialVersionUID = 8876966522510157497L; |
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77 |
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78 /** |
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79 * Determines whether a Component is an acceptable choice as the new |
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80 * focus owner. The Component must be visible, displayable, and enabled |
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81 * to be accepted. If client code has explicitly set the focusability |
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82 * of the Component by either overriding |
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83 * <code>Component.isFocusTraversable()</code> or |
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84 * <code>Component.isFocusable()</code>, or by calling |
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85 * <code>Component.setFocusable()</code>, then the Component will be |
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86 * accepted if and only if it is focusable. If, however, the Component is |
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87 * relying on default focusability, then all Canvases, Labels, Panels, |
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88 * Scrollbars, ScrollPanes, Windows, and lightweight Components will be |
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89 * rejected. |
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90 * |
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91 * @param aComponent the Component whose fitness as a focus owner is to |
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92 * be tested |
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93 * @return <code>true</code> if aComponent meets the above requirements; |
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94 * <code>false</code> otherwise |
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95 */ |
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96 protected boolean accept(Component aComponent) { |
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97 if (!(aComponent.isVisible() && aComponent.isDisplayable() && |
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98 aComponent.isEnabled())) |
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99 { |
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100 return false; |
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101 } |
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102 |
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103 // Verify that the Component is recursively enabled. Disabling a |
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104 // heavyweight Container disables its children, whereas disabling |
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105 // a lightweight Container does not. |
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106 if (!(aComponent instanceof Window)) { |
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107 for (Container enableTest = aComponent.getParent(); |
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108 enableTest != null; |
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109 enableTest = enableTest.getParent()) |
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110 { |
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111 if (!(enableTest.isEnabled() || enableTest.isLightweight())) { |
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112 return false; |
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113 } |
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114 if (enableTest instanceof Window) { |
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115 break; |
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116 } |
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117 } |
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118 } |
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119 |
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120 boolean focusable = aComponent.isFocusable(); |
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121 if (aComponent.isFocusTraversableOverridden()) { |
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122 return focusable; |
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123 } |
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124 |
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125 ComponentPeer peer = aComponent.getPeer(); |
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126 return (peer != null && peer.isFocusable()); |
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127 } |
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128 } |