defaultfocustraversalpolicy.java

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/*
 * 
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 only, as published by the Free Software Foundation. 
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License version 2 for more details (a copy is
 * included at /legal/license.txt). 
 * 
 * You should have received a copy of the GNU General Public License
 * version 2 along with this work; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA 
 * 
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
 * Clara, CA 95054 or visit www.sun.com if you need additional
 * information or have any questions. 
 */
package java.awt;

/**
 * A FocusTraversalPolicy that determines traversal order based on the order
 * of child Components in a Container. From a particular focus cycle root, the
 * policy makes a pre-order traversal of the Component hierarchy, and traverses
 * a Container's children according to the ordering of the array returned by
 * <code>Container.getComponents()</code>. Portions of the hierarchy that are
 * not visible and displayable will not be searched.
 * <p>
 * If client code has explicitly set the focusability of a Component by either
 * overriding <code>Component.isFocusTraversable()</code> or
 * <code>Component.isFocusable()</code>, or by calling
 * <code>Component.setFocusable()</code>, then a DefaultFocusTraversalPolicy
 * behaves exactly like a ContainerOrderFocusTraversalPolicy. If, however, the
 * Component is relying on default focusability, then a
 * DefaultFocusTraversalPolicy will reject all Components with non-focusable
 * peers. This is the default FocusTraversalPolicy for all AWT Containers.
 * <p>
 * The focusability of a peer is implementation-dependent. Sun recommends that
 * all implementations for a particular native platform construct peers with
 * the same focusability. The recommendations for Windows and Unix are that
 * Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight
 * Components have non-focusable peers, and all other Components have focusable
 * peers. These recommendations are used in the Sun AWT implementations. Note
 * that the focusability of a Component's peer is different from, and does not
 * impact, the focusability of the Component itself.
 *
 * @author David Mendenhall
 * @version 1.3, 01/23/03
 *
 * @see Container#getComponents
 * @see Component#isFocusable
 * @see Component#setFocusable
 * @since 1.4
 */
public class DefaultFocusTraversalPolicy extends ContainerOrderFocusTraversalPolicy {
    /**
     * Determines whether a Component is an acceptable choice as the new
     * focus owner. The Component must be visible, displayable, and enabled
     * to be accepted. If client code has explicitly set the focusability
     * of the Component by either overriding
     * <code>Component.isFocusTraversable()</code> or
     * <code>Component.isFocusable()</code>, or by calling
     * <code>Component.setFocusable()</code>, then the Component will be
     * accepted if and only if it is focusable. If, however, the Component is
     * relying on default focusability, then all Canvases, Labels, Panels,
     * Scrollbars, ScrollPanes, Windows, and lightweight Components will be
     * rejected.
     *
     * @param aComponent the Component whose fitness as a focus owner is to
     *        be tested
     * @return <code>true</code> if aComponent meets the above requirements;
     *         <code>false</code> otherwise
     */
    protected boolean accept(Component aComponent) {
        if (!(aComponent.isVisible() && aComponent.isDisplayable()
                && aComponent.isEnabled())) {
            return false;
        }
        // Verify that the Component is recursively enabled. Disabling a
        // heavyweight Container disables its children, whereas disabling
        // a lightweight Container does not.
        if (!(aComponent instanceof Window)) {
            for (Container enableTest = aComponent.getParent();
                    enableTest != null;
                    enableTest = enableTest.getParent()) {
                if (!(enableTest.isEnabled() || enableTest.isLightweight())) {
                    return false;
                }
                if (enableTest instanceof Window) {
                    break;
                }
            }
        }
        boolean focusable = aComponent.isFocusable();
        if (aComponent.isFocusTraversableOverridden()) {
            return focusable;
        }
        return false;
    }
}