/*

 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 in the LICENSE file that

 * accompanied this code).

 *

 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.awt;

import java.awt.peer.ComponentPeer;

/**

 * 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.

 * <p>

 * Please see

 * <a href="https://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html">

 * How to Use the Focus Subsystem</a>,

 * a section in <em>The Java Tutorial</em>, and the

 * <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>

 * for more information.

 *

 * @author David Mendenhall

 *

 * @see Container#getComponents

 * @see Component#isFocusable

 * @see Component#setFocusable

 * @since 1.4

 */

public class DefaultFocusTraversalPolicy

    extends ContainerOrderFocusTraversalPolicy

{

    /*

     * serialVersionUID

     */

    private static final long serialVersionUID = 8876966522510157497L;

    /**

     * 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;

        }

        ComponentPeer peer = aComponent.getPeer();

        return (peer != null && peer.isFocusable());

    }

}