1 /* 2 * Copyright (c) 2000, 2005, 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 /** 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="http://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 }