src/java.desktop/share/classes/javax/swing/LayoutFocusTraversalPolicy.java

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package javax.swing;

import java.awt.Component;
import java.awt.Container;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serial;
import java.io.Serializable;
import java.util.Comparator;
import java.util.Enumeration;

import sun.awt.SunToolkit;

/**
 * A SortingFocusTraversalPolicy which sorts Components based on their size,
 * position, and orientation. Based on their size and position, Components are
 * roughly categorized into rows and columns. For a Container with horizontal
 * orientation, columns run left-to-right or right-to-left, and rows run top-
 * to-bottom. For a Container with vertical orientation, columns run top-to-
 * bottom and rows run left-to-right or right-to-left. See
 * <code>ComponentOrientation</code> for more information. All columns in a
 * row are fully traversed before proceeding to the next row.
 *
 * @author David Mendenhall
 *
 * @see java.awt.ComponentOrientation
 * @since 1.4
 */
@SuppressWarnings("serial") // Parts of superclass are not serializable across versions
public class LayoutFocusTraversalPolicy extends SortingFocusTraversalPolicy
    implements Serializable
{
    // Delegate most of our fitness test to Default so that we only have to
    // code the algorithm once.
    private static final SwingDefaultFocusTraversalPolicy fitnessTestPolicy =
        new SwingDefaultFocusTraversalPolicy();

    /**
     * Constructs a LayoutFocusTraversalPolicy.
     */
    public LayoutFocusTraversalPolicy() {
        super(new LayoutComparator());
    }

    /**
     * Constructs a LayoutFocusTraversalPolicy with the passed in
     * <code>Comparator</code>.
     */
    LayoutFocusTraversalPolicy(Comparator<? super Component> c) {
        super(c);
    }

    /**
     * Returns the Component that should receive the focus after aComponent.
     * aContainer must be a focus cycle root of aComponent.
     * <p>
     * By default, LayoutFocusTraversalPolicy implicitly transfers focus down-
     * cycle. That is, during normal focus traversal, the Component
     * traversed after a focus cycle root will be the focus-cycle-root's
     * default Component to focus. This behavior can be disabled using the
     * <code>setImplicitDownCycleTraversal</code> method.
     * <p>
     * If aContainer is <a href="../../java/awt/doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus
     * traversal policy provider</a>, the focus is always transferred down-cycle.
     *
     * @param aContainer a focus cycle root of aComponent or a focus traversal policy provider
     * @param aComponent a (possibly indirect) child of aContainer, or
     *        aContainer itself
     * @return the Component that should receive the focus after aComponent, or
     *         null if no suitable Component can be found
     * @throws IllegalArgumentException if aContainer is not a focus cycle
     *         root of aComponent or a focus traversal policy provider, or if either aContainer or
     *         aComponent is null
     */
    public Component getComponentAfter(Container aContainer,
                                       Component aComponent) {
        if (aContainer == null || aComponent == null) {
            throw new IllegalArgumentException("aContainer and aComponent cannot be null");
        }
        Comparator<? super Component> comparator = getComparator();
        if (comparator instanceof LayoutComparator) {
            ((LayoutComparator)comparator).
                setComponentOrientation(aContainer.
                                        getComponentOrientation());
        }
        return super.getComponentAfter(aContainer, aComponent);
    }

    /**
     * Returns the Component that should receive the focus before aComponent.
     * aContainer must be a focus cycle root of aComponent.
     * <p>
     * By default, LayoutFocusTraversalPolicy implicitly transfers focus down-
     * cycle. That is, during normal focus traversal, the Component
     * traversed after a focus cycle root will be the focus-cycle-root's
     * default Component to focus. This behavior can be disabled using the
     * <code>setImplicitDownCycleTraversal</code> method.
     * <p>
     * If aContainer is <a href="../../java/awt/doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus
     * traversal policy provider</a>, the focus is always transferred down-cycle.
     *
     * @param aContainer a focus cycle root of aComponent or a focus traversal policy provider
     * @param aComponent a (possibly indirect) child of aContainer, or
     *        aContainer itself
     * @return the Component that should receive the focus before aComponent,
     *         or null if no suitable Component can be found
     * @throws IllegalArgumentException if aContainer is not a focus cycle
     *         root of aComponent or a focus traversal policy provider, or if either aContainer or
     *         aComponent is null
     */
    public Component getComponentBefore(Container aContainer,
                                        Component aComponent) {
        if (aContainer == null || aComponent == null) {
            throw new IllegalArgumentException("aContainer and aComponent cannot be null");
        }
        Comparator<? super Component> comparator = getComparator();
        if (comparator instanceof LayoutComparator) {
            ((LayoutComparator)comparator).
                setComponentOrientation(aContainer.
                                        getComponentOrientation());
        }
        return super.getComponentBefore(aContainer, aComponent);
    }

    /**
     * Returns the first Component in the traversal cycle. This method is used
     * to determine the next Component to focus when traversal wraps in the
     * forward direction.
     *
     * @param aContainer a focus cycle root of aComponent or a focus traversal policy provider whose
     *        first Component is to be returned
     * @return the first Component in the traversal cycle of aContainer,
     *         or null if no suitable Component can be found
     * @throws IllegalArgumentException if aContainer is null
     */
    public Component getFirstComponent(Container aContainer) {
        if (aContainer == null) {
            throw new IllegalArgumentException("aContainer cannot be null");
        }
        Comparator<? super Component> comparator = getComparator();
        if (comparator instanceof LayoutComparator) {
            ((LayoutComparator)comparator).
                setComponentOrientation(aContainer.
                                        getComponentOrientation());
        }
        return super.getFirstComponent(aContainer);
    }

    /**
     * Returns the last Component in the traversal cycle. This method is used
     * to determine the next Component to focus when traversal wraps in the
     * reverse direction.
     *
     * @param aContainer a focus cycle root of aComponent or a focus traversal policy provider whose
     *        last Component is to be returned
     * @return the last Component in the traversal cycle of aContainer,
     *         or null if no suitable Component can be found
     * @throws IllegalArgumentException if aContainer is null
     */
    public Component getLastComponent(Container aContainer) {
        if (aContainer == null) {
            throw new IllegalArgumentException("aContainer cannot be null");
        }
        Comparator<? super Component> comparator = getComparator();
        if (comparator instanceof LayoutComparator) {
            ((LayoutComparator)comparator).
                setComponentOrientation(aContainer.
                                        getComponentOrientation());
        }
        return super.getLastComponent(aContainer);
    }

    /**
     * Determines whether the specified <code>Component</code>
     * is an acceptable choice as the new focus owner.
     * This method performs the following sequence of operations:
     * <ol>
     * <li>Checks whether <code>aComponent</code> is visible, displayable,
     *     enabled, and focusable.  If any of these properties is
     *     <code>false</code>, this method returns <code>false</code>.
     * <li>If <code>aComponent</code> is an instance of <code>JTable</code>,
     *     returns <code>true</code>.
     * <li>If <code>aComponent</code> is an instance of <code>JComboBox</code>,
     *     then returns the value of
     *     <code>aComponent.getUI().isFocusTraversable(aComponent)</code>.
     * <li>If <code>aComponent</code> is a <code>JComponent</code>
     *     with a <code>JComponent.WHEN_FOCUSED</code>
     *     <code>InputMap</code> that is neither <code>null</code>
     *     nor empty, returns <code>true</code>.
     * <li>Returns the value of
     *     <code>DefaultFocusTraversalPolicy.accept(aComponent)</code>.
     * </ol>
     *
     * @param aComponent the <code>Component</code> whose fitness
     *                   as a focus owner is to be tested
     * @see java.awt.Component#isVisible
     * @see java.awt.Component#isDisplayable
     * @see java.awt.Component#isEnabled
     * @see java.awt.Component#isFocusable
     * @see javax.swing.plaf.ComboBoxUI#isFocusTraversable
     * @see javax.swing.JComponent#getInputMap
     * @see java.awt.DefaultFocusTraversalPolicy#accept
     * @return <code>true</code> if <code>aComponent</code> is a valid choice
     *         for a focus owner;
     *         otherwise <code>false</code>
     */
     protected boolean accept(Component aComponent) {
        if (!super.accept(aComponent)) {
            return false;
        } else if (SunToolkit.isInstanceOf(aComponent, "javax.swing.JTable")) {
            // JTable only has ancestor focus bindings, we thus force it
            // to be focusable by returning true here.
            return true;
        } else if (SunToolkit.isInstanceOf(aComponent, "javax.swing.JComboBox")) {
            JComboBox<?> box = (JComboBox)aComponent;
            return box.getUI().isFocusTraversable(box);
        } else if (aComponent instanceof JComponent) {
            if (SunToolkit.isInstanceOf(aComponent,
                                                 "javax.swing.JToggleButton")) {
                ButtonModel model = ((JToggleButton)aComponent).getModel();
                if (model != null) {
                    ButtonGroup group = model.getGroup();
                    if (group != null) {
                        Enumeration<AbstractButton> elements =
                                                        group.getElements();
                        int idx = 0;
                        while (elements.hasMoreElements()) {
                            AbstractButton member = elements.nextElement();
                            if (member instanceof JToggleButton &&
                                 member.isVisible() && member.isDisplayable() &&
                                 member.isEnabled() && member.isFocusable()) {
                                if (member == aComponent) {
                                    return idx == 0;
                                }
                                idx++;
                            }
                        }
                    }
                }
            }

            JComponent jComponent = (JComponent)aComponent;
            InputMap inputMap = jComponent.getInputMap(JComponent.WHEN_FOCUSED,
                                                       false);
            while (inputMap != null && inputMap.size() == 0) {
                inputMap = inputMap.getParent();
            }
            if (inputMap != null) {
                return true;
            }
            // Delegate to the fitnessTestPolicy, this will test for the
            // case where the developer has overridden isFocusTraversable to
            // return true.
        }
        return fitnessTestPolicy.accept(aComponent);
    }

    @Serial
    private void writeObject(ObjectOutputStream out) throws IOException {
        out.writeObject(getComparator());
        out.writeBoolean(getImplicitDownCycleTraversal());
    }
    @Serial
    @SuppressWarnings("unchecked") // Cast to (Comparator<? super Component>)
    private void readObject(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        setComparator((Comparator<? super Component>)in.readObject());
        setImplicitDownCycleTraversal(in.readBoolean());
    }
}

// Create our own subclass and change accept to public so that we can call
// accept.
@SuppressWarnings("serial") // JDK-implementation class
class SwingDefaultFocusTraversalPolicy
    extends java.awt.DefaultFocusTraversalPolicy
{
    public boolean accept(Component aComponent) {
        return super.accept(aComponent);
    }
}