/*
 
* Copyright (c) 1997, 2013, 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=" 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 .
 
*
 
* @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&amp;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&amp;F) object that renders this component.
     
*
     
* @param ui
  
the PanelUI L&amp;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&amp;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&amp;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&trade;
     
* has been added to the <code>java.beans</code> package.
     
* Please see
 
.
     
*/

    
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;
        
}
    
}
}