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 * Copyright (c) 1997, 2015, 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 javax.swing;

import java.awt.*;
import java.beans.JavaBean;
import java.beans.BeanProperty;

import javax.swing.plaf.*;
import javax.accessibility.*;

import java.io.ObjectOutputStream;
import java.io.IOException;


JPanel is a generic lightweight container.
For examples and task-oriented documentation for JPanel, see
How to Use Panels,
a section in The Java Tutorial.

Warning: Swing is not thread safe. For more
information see Swing's Threading
Policy.

Warning:
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™
has been added to the java.beans package. Please see XMLEncoder. 
Author:
Arnaud Weber, Steve Wilson
Since:
1.2/**
 * <code>JPanel</code> is a generic lightweight container.
 * For examples and task-oriented documentation for JPanel, see
 * <a
 href="https://docs.oracle.com/javase/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&trade;
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @author Arnaud Weber
 * @author Steve Wilson
 * @since 1.2
 */
@JavaBean(defaultProperty = "UI", description = "A generic lightweight container.")
@SuppressWarnings("serial") // Same-version serialization only
public class JPanel extends JComponent implements Accessible
{
    
See Also:
getUIClassID
JComponent.readObject/**
     * @see #getUIClassID
     * @see #readObject
     */
    private static final String uiClassID = "PanelUI";

    
Creates a new JPanel with the specified layout manager and buffering
strategy.
Params:
layout –  the LayoutManager to use
isDoubleBuffered –  a boolean, true for double-buffering, which
       uses additional memory space to achieve fast, flicker-free
       updates/**
     * 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
Params:
layout –  the LayoutManager to use/**
     * 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 JPanel with FlowLayout
and the specified buffering strategy.
If isDoubleBuffered is true, the JPanel
will use a double buffer.
Params:
isDoubleBuffered –  a boolean, true for double-buffering, which
       uses additional memory space to achieve fast, flicker-free
       updates/**
     * 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 JPanel with a double buffer
and a flow layout.
/**
     * 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 Also:
updateUI.updateUI/**
     * 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.
Returns:
the PanelUI object that renders this component
Since:
1.4/**
     * Returns the look and feel (L&amp;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.
Params:
ui –  the PanelUI L&F object
See Also:
UIDefaults.getUI
Since:
1.4/**
     * Sets the look and feel (L&amp;F) object that renders this component.
     *
     * @param ui  the PanelUI L&amp;F object
     * @see UIDefaults#getUI
     * @since 1.4
     */
    @BeanProperty(hidden = true, 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.
See Also:
JComponent.getUIClassID
UIDefaults.getUI
Returns:
the string "PanelUI"/**
     * Returns a string that specifies the name of the L&amp;F class
     * that renders this component.
     *
     * @return the string "PanelUI"
     * @see JComponent#getUIClassID
     * @see UIDefaults#getUI
     */
    @BeanProperty(bound = false, 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.
/**
     * 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 null.
Returns:
 a string representation of this JPanel./**
     * 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.
Returns:
an AccessibleJPanel that serves as the
        AccessibleContext of this JPanel/**
     * 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
     */
    @BeanProperty(bound = false)
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleJPanel();
        }
        return accessibleContext;
    }

    
This class implements accessibility support for the
JPanel class.  It provides an implementation of the
Java Accessibility API appropriate to panel user-interface
elements.

Warning:
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™
has been added to the java.beans package. Please see XMLEncoder. /**
     * 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&trade;
     * has been added to the <code>java.beans</code> package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    @SuppressWarnings("serial") // Same-version serialization only
    protected class AccessibleJPanel extends AccessibleJComponent {

        
Get the role of this object.
Returns:
an instance of AccessibleRole describing the role of the
object/**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the
         * object
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.PANEL;
        }
    }
}