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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());
 }
}