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 JavaBeansTM
* has been added to the java.beans 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 JPanel with FlowLayout
* and the specified buffering strategy.
* If isDoubleBuffered is true, the JPanel
* 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.
*/
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 null.
*
* @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
* 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 JavaBeansTM
* has been added to the java.beans 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;
}
}
}