src/java.desktop/share/classes/javax/swing/plaf/basic/DefaultMenuLayout.java

/*
 * Copyright (c) 1998, 2014, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing.plaf.basic;

import javax.swing.*;
import javax.swing.plaf.UIResource;

import java.awt.Container;
import java.awt.Dimension;

/**
 * The default layout manager for Popup menus and menubars.  This
 * class is an extension of BoxLayout which adds the UIResource tag
 * so that pluggable L&Fs can distinguish it from user-installed
 * layout managers on menus.
 *
 * @author Georges Saab
 */
@SuppressWarnings("serial") // Superclass is not serializable across versions
public class DefaultMenuLayout extends BoxLayout implements UIResource {

    /**
     * Constructs a new instance of {@code DefaultMenuLayout}.
     *
     * @param target the container that needs to be laid out
     * @param axis the axis to lay out components along. Can be one of:
     *              {@code BoxLayout.X_AXIS},
     *              {@code BoxLayout.Y_AXIS},
     *              {@code BoxLayout.LINE_AXIS} or
     *              {@code BoxLayout.PAGE_AXIS}
     */
    public DefaultMenuLayout(Container target, int axis) {
        super(target, axis);
    }

    public Dimension preferredLayoutSize(Container target) {
        if (target instanceof JPopupMenu) {
            JPopupMenu popupMenu = (JPopupMenu) target;
            sun.swing.MenuItemLayoutHelper.clearUsedClientProperties(popupMenu);
            if (popupMenu.getComponentCount() == 0) {
                return new Dimension(0, 0);
            }
        }

        // Make BoxLayout recalculate cached preferred sizes
        super.invalidateLayout(target);

        return super.preferredLayoutSize(target);
    }
}