/*

 * Copyright (c) 1997, 2006, 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;

import java.awt.*;

import javax.swing.plaf.*;

import javax.accessibility.*;

import java.io.Serializable;

import java.io.ObjectOutputStream;

import java.io.ObjectInputStream;

import java.io.IOException;

/**

 * <code>JPanel</code> is a generic lightweight container.

 * For examples and task-oriented documentation for JPanel, see

 * <a

 href="http://java.sun.com/docs/books/tutorial/uiswing/components/panel.html">How to Use Panels</a>,

 * a section in <em>The Java Tutorial</em>.

 * <p>

 * <strong>Warning:</strong> Swing is not thread safe. For more

 * information see <a

 * href="package-summary.html#threading">Swing's Threading

 * Policy</a>.

 * <p>

 * <strong>Warning:</strong>

 * Serialized objects of this class will not be compatible with

 * future Swing releases. The current serialization support is

 * appropriate for short term storage or RMI between applications running

 * the same version of Swing.  As of 1.4, support for long term storage

 * of all JavaBeans<sup><font size="-2">TM</font></sup>

 * has been added to the <code>java.beans</code> package.

 * Please see {@link java.beans.XMLEncoder}.

 *

 * @beaninfo

 * description: A generic lightweight container.

 *

 * @author Arnaud Weber

 * @author Steve Wilson

 */

public class JPanel extends JComponent implements Accessible

{

    /**

     * @see #getUIClassID

     * @see #readObject

     */

    private static final String uiClassID = "PanelUI";

    /**

     * Creates a new JPanel with the specified layout manager and buffering

     * strategy.

     *

     * @param layout  the LayoutManager to use

     * @param isDoubleBuffered  a boolean, true for double-buffering, which

     *        uses additional memory space to achieve fast, flicker-free

     *        updates

     */

    public JPanel(LayoutManager layout, boolean isDoubleBuffered) {

        setLayout(layout);

        setDoubleBuffered(isDoubleBuffered);

        setUIProperty("opaque", Boolean.TRUE);

        updateUI();

    }

    /**

     * Create a new buffered JPanel with the specified layout manager

     *

     * @param layout  the LayoutManager to use

     */

    public JPanel(LayoutManager layout) {

        this(layout, true);

    }

    /**

     * Creates a new <code>JPanel</code> with <code>FlowLayout</code>

     * and the specified buffering strategy.

     * If <code>isDoubleBuffered</code> is true, the <code>JPanel</code>

     * will use a double buffer.

     *

     * @param isDoubleBuffered  a boolean, true for double-buffering, which

     *        uses additional memory space to achieve fast, flicker-free

     *        updates

     */

    public JPanel(boolean isDoubleBuffered) {

        this(new FlowLayout(), isDoubleBuffered);

    }

    /**

     * Creates a new <code>JPanel</code> with a double buffer

     * and a flow layout.

     */

    public JPanel() {

        this(true);

    }

    /**

     * Resets the UI property with a value from the current look and feel.

     *

     * @see JComponent#updateUI

     */

    public void updateUI() {

        setUI((PanelUI)UIManager.getUI(this));

    }

    /**

     * Returns the look and feel (L&F) object that renders this component.

     *

     * @return the PanelUI object that renders this component

     * @since 1.4

     */

    public PanelUI getUI() {

        return (PanelUI)ui;

    }

    /**

     * Sets the look and feel (L&F) object that renders this component.

     *

     * @param ui  the PanelUI L&F object

     * @see UIDefaults#getUI

     * @since 1.4

     * @beaninfo

     *        bound: true

     *       hidden: true

     *    attribute: visualUpdate true

     *  description: The UI object that implements the Component's LookAndFeel.

     */

    public void setUI(PanelUI ui) {

        super.setUI(ui);

    }

    /**

     * Returns a string that specifies the name of the L&F class

     * that renders this component.

     *

     * @return "PanelUI"

     * @see JComponent#getUIClassID

     * @see UIDefaults#getUI

     * @beaninfo

     *        expert: true

     *   description: A string that specifies the name of the L&F class.

     */

    public String getUIClassID() {

        return uiClassID;

    }

    /**

     * See readObject() and writeObject() in JComponent for more

     * information about serialization in Swing.

     */

    private void writeObject(ObjectOutputStream s) throws IOException {

        s.defaultWriteObject();

        if (getUIClassID().equals(uiClassID)) {

            byte count = JComponent.getWriteObjCounter(this);

            JComponent.setWriteObjCounter(this, --count);

            if (count == 0 && ui != null) {

                ui.installUI(this);

            }

        }

    }

    /**

     * Returns a string representation of this JPanel. This method

     * is intended to be used only for debugging purposes, and the

     * content and format of the returned string may vary between

     * implementations. The returned string may be empty but may not

     * be <code>null</code>.

     *

     * @return  a string representation of this JPanel.

     */

    protected String paramString() {

        return super.paramString();

    }

/////////////////

// Accessibility support

////////////////

    /**

     * Gets the AccessibleContext associated with this JPanel.

     * For JPanels, the AccessibleContext takes the form of an

     * AccessibleJPanel.

     * A new AccessibleJPanel instance is created if necessary.

     *

     * @return an AccessibleJPanel that serves as the

     *         AccessibleContext of this JPanel

     */

    public AccessibleContext getAccessibleContext() {

        if (accessibleContext == null) {

            accessibleContext = new AccessibleJPanel();

        }

        return accessibleContext;

    }

    /**

     * This class implements accessibility support for the

     * <code>JPanel</code> class.  It provides an implementation of the

     * Java Accessibility API appropriate to panel user-interface

     * elements.

     * <p>

     * <strong>Warning:</strong>

     * Serialized objects of this class will not be compatible with

     * future Swing releases. The current serialization support is

     * appropriate for short term storage or RMI between applications running

     * the same version of Swing.  As of 1.4, support for long term storage

     * of all JavaBeans<sup><font size="-2">TM</font></sup>

     * has been added to the <code>java.beans</code> package.

     * Please see {@link java.beans.XMLEncoder}.

     */

    protected class AccessibleJPanel extends AccessibleJComponent {

        /**

         * Get the role of this object.

         *

         * @return an instance of AccessibleRole describing the role of the

         * object

         */

        public AccessibleRole getAccessibleRole() {

            return AccessibleRole.PANEL;

        }

    }

}