ComponentUI (GNU Classpath 0.94-pre Documentation)

The abstract base class for all delegates that provide the pluggable look and feel for Swing components. User applications should not need to access this class; it is internal to Swing and the look-and-feel implementations.

[UML diagram illustrating the architecture for pluggable
look and feels]

Components such as {@link javax.swing.JSlider} do not directly implement operations related to the look and feel of the user interface, such as painting or layout. Instead, they use a delegate object for all such tasks. In the case of JSlider, the user interface would be provided by some concrete subclass of {@link javax.swing.plaf.SliderUI}.

Soon after its creation, a ComponentUI will be sent an {@link #installUI} message. The ComponentUI will react by setting properties such as the border or the background color of the JComponent for which it provides its services. Soon before the end of its lifecycle, the ComponentUI will receive an {@link #uninstallUI} message, at which time the ComponentUI is expected to undo any changes.

Note that the ui of a JComponent changes whenever the user switches between look and feels. For example, the ui property of a JSlider could change from an instance of MetalSliderUI to an instance of FooSliderUI. This switch can happen at any time, but it will always be performed from inside the Swing thread.

Constructor Summary
	ComponentUI() Constructs a new UI delegate.

Method Summary
boolean	contains(JComponent c, int x, int y) Determines whether a click into the component at a specified location is considered as having hit the component.
static ComponentUI	createUI(JComponent c) Creates a delegate object for the specified component.
Accessible	getAccessibleChild(JComponent c, int i) Returns the specified accessible child of the component.
int	getAccessibleChildrenCount(JComponent c) Counts the number of accessible children in the component.
Dimension	getMaximumSize(JComponent c) Determines the maximum size of a component.
Dimension	getMinimumSize(JComponent c) Determines the minimum size of a component.
Dimension	getPreferredSize(JComponent c) Determines the preferred size of a component.
void	installUI(JComponent c) Sets up the specified component so it conforms the the design guidelines of the implemented look and feel.
void	paint(Graphics g, JComponent c) Paints the component according to the design guidelines of the look and feel.
void	uninstallUI(JComponent c) Puts the specified component into the state it had before {@link #installUI} was called.
void	update(Graphics g, JComponent c) Fills the specified component with its background color (unless the `opaque` property is `false`) before calling {@link #paint}.

Determines whether a click into the component at a specified location is considered as having hit the component. The default implementation checks whether the point falls into the component’s bounding rectangle. Some subclasses might want to override this, for example in the case of a rounded button.

Parameters: c the component for which this delegate performs services. x the x coordinate of the point, relative to the local coordinate system of the component. Zero would be be component’s left edge, irrespective of the location inside its parent. y the y coordinate of the point, relative to the local coordinate system of the component. Zero would be be component’s top edge, irrespective of the location inside its parent.

createUI

getAccessibleChild

Returns the specified accessible child of the component. The default implementation delegates the inquiry to the {@link javax.accessibility.AccessibleContext} of c.

Parameters: i the index of the accessible child, starting at zero. c the component whose i-th accessible child is requested.

getAccessibleChildrenCount

getMaximumSize

Determines the maximum size of a component. The default implementation calls {@link #getPreferredSize}, but subclasses might want to override this.

Parameters: c the component for which this delegate performs services.

Returns: the maximum size, or null to indicate that c’s layout manager should be asked to calculate the maximum size.

getMinimumSize

Determines the minimum size of a component. The default implementation calls {@link #getPreferredSize}, but subclasses might want to override this.

Parameters: c the component for which this delegate performs services.

Returns: the minimum size, or null to indicate that c’s layout manager should be asked to calculate the minimum size.

getPreferredSize

Determines the preferred size of a component. The default implementation returns null, which means that c’s layout manager should be asked to calculate the preferred size.

Parameters: c the component for which this delegate performs services.

Returns: the preferred size, or null to indicate that c’s layout manager should be asked for the preferred size.

installUI

Sets up the specified component so it conforms the the design guidelines of the implemented look and feel. When the look and feel changes, a ComponentUI delegate is created. The delegate object then receives an installUI message.

This method should perform the following tasks:

Set visual properties such as borders, fonts, colors, or icons. However, no change should be performed for those properties whose values have been directly set by the client application. To allow the distinction, LookAndFeels are expected to use values that implement the {@link UIResource} marker interface, such as {@link BorderUIResource} or {@link ColorUIResource}.
If necessary, install a {@link java.awt.LayoutManager}.
Embed custom sub-components. For instance, the UI delegate for a {@link javax.swing.JSplitPane} might install a special component for the divider.
Register event listeners.
Set up properties related to keyborad navigation, such as mnemonics or focus traversal policies.

Parameters: c the component for which this delegate will provide services.

paint

uninstallUI

update

Fills the specified component with its background color (unless the opaque property is false) before calling {@link #paint}.

It is unlikely that a subclass needs to override this method. The actual rendering should be performed by the {@link #paint} method.

Parameters: g the graphics for painting. c the component for which this delegate performs services.

Class ComponentUI