Module java.desktop
Package javax.swing

Class JComponent

All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable
Direct Known Subclasses:
AbstractButton, BasicInternalFrameTitlePane, Box, Box.Filler, JColorChooser, JComboBox, JFileChooser, JInternalFrame, JInternalFrame.JDesktopIcon, JLabel, JLayer, JLayeredPane, JList, JMenuBar, JOptionPane, JPanel, JPopupMenu, JProgressBar, JRootPane, JScrollBar, JScrollPane, JSeparator, JSlider, JSpinner, JSplitPane, JTabbedPane, JTable, JTableHeader, JTextComponent, JToolBar, JToolTip, JTree, JViewport

@JavaBean(defaultProperty="UIClassID") public abstract class JComponent extends Container implements Serializable
The base class for all Swing components except top-level containers. To use a component that inherits from JComponent, you must place the component in a containment hierarchy whose root is a top-level Swing container. Top-level Swing containers -- such as JFrame, JDialog, and JApplet -- are specialized components that provide a place for other Swing components to paint themselves. For an explanation of containment hierarchies, see Swing Components and the Containment Hierarchy, a section in The Java Tutorial.

The JComponent class provides:

  • The base class for both standard and custom components that use the Swing architecture.
  • A "pluggable look and feel" (L&F) that can be specified by the programmer or (optionally) selected by the user at runtime. The look and feel for each component is provided by a UI delegate -- an object that descends from ComponentUI. See How to Set the Look and Feel in The Java Tutorial for more information.
  • Comprehensive keystroke handling. See the document How to Use Key Bindings, an article in The Java Tutorial, for more information.
  • Support for tool tips -- short descriptions that pop up when the cursor lingers over a component. See How to Use Tool Tips in The Java Tutorial for more information.
  • Support for accessibility. JComponent contains all of the methods in the Accessible interface, but it doesn't actually implement the interface. That is the responsibility of the individual classes that extend JComponent.
  • Support for component-specific properties. With the putClientProperty(java.lang.Object, java.lang.Object) and getClientProperty(java.lang.Object) methods, you can associate name-object pairs with any object that descends from JComponent.
  • An infrastructure for painting that includes double buffering and support for borders. For more information see Painting and How to Use Borders, both of which are sections in The Java Tutorial.
For more information on these subjects, see the Swing package description and The Java Tutorial section The JComponent Class.

JComponent and its subclasses document default values for certain properties. For example, JTable documents the default row height as 16. Each JComponent subclass that has a ComponentUI will create the ComponentUI as part of its constructor. In order to provide a particular look and feel each ComponentUI may set properties back on the JComponent that created it. For example, a custom look and feel may require JTables to have a row height of 24. The documented defaults are the value of a property BEFORE the ComponentUI has been installed. If you need a specific value for a particular property you should explicitly set it.

A JComponent may contain any number of default or initial components as children. This behaviour may change according to look and feel, therefore a JComponent may contain some default or initial components as children for a particular Look and Feel, whereas it may not do so for some other Look and Feel. Within a particular Look and Feel also, this behaviour may change depending upon the configuration properties of the JComponent. In summary, it is not valid to assume a JComponent has no children just because the application did not directly add them.

In release 1.4, the focus subsystem was rearchitected. For more information, see How to Use the Focus Subsystem, 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.

See Also: