javax.swing.plaf
Class ComponentUI

java.lang.Object
  extended by javax.swing.plaf.ComponentUI
Direct Known Subclasses:
ButtonUI, ColorChooserUI, ComboBoxUI, DesktopIconUI, DesktopPaneUI, FileChooserUI, InternalFrameUI, LabelUI, ListUI, MenuBarUI, OptionPaneUI, PanelUI, PopupMenuUI, ProgressBarUI, RootPaneUI, ScrollBarUI, ScrollPaneUI, SeparatorUI, SliderUI, SpinnerUI, SplitPaneUI, TabbedPaneUI, TableHeaderUI, TableUI, TextUI, ToolBarUI, ToolTipUI, TreeUI, ViewportUI

public abstract class ComponentUI
extends Object

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 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 SliderUI.

Soon after its creation, a ComponentUI will be sent an installUI(javax.swing.JComponent) 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 uninstallUI(javax.swing.JComponent) 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 installUI(javax.swing.JComponent) was called.
 void update(Graphics g, JComponent c)
          Fills the specified component with its background color (unless the opaque property is false) before calling paint(java.awt.Graphics, javax.swing.JComponent).
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

ComponentUI

public ComponentUI()
Constructs a new UI delegate.

Method Detail

installUI

public void installUI(JComponent c)
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:

Parameters:
c - the component for which this delegate will provide services.
See Also:
uninstallUI(javax.swing.JComponent), JComponent.setUI(javax.swing.plaf.ComponentUI), JComponent.updateUI()

uninstallUI

public void uninstallUI(JComponent c)
Puts the specified component into the state it had before installUI(javax.swing.JComponent) was called.

Parameters:
c - the component for which this delegate has provided services.
See Also:
installUI(javax.swing.JComponent), JComponent.setUI(javax.swing.plaf.ComponentUI), JComponent.updateUI()

paint

public void paint(Graphics g,
                  JComponent c)
Paints the component according to the design guidelines of the look and feel. Most subclasses will want to override this method.

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

update

public void update(Graphics g,
                   JComponent c)
Fills the specified component with its background color (unless the opaque property is false) before calling paint(java.awt.Graphics, javax.swing.JComponent).

It is unlikely that a subclass needs to override this method. The actual rendering should be performed by the paint(java.awt.Graphics, javax.swing.JComponent) method.

Parameters:
g - the graphics for painting.
c - the component for which this delegate performs services.
See Also:
paint(java.awt.Graphics, javax.swing.JComponent), JComponent.paintComponent(java.awt.Graphics)

getPreferredSize

public Dimension getPreferredSize(JComponent c)
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.

getMinimumSize

public Dimension getMinimumSize(JComponent c)
Determines the minimum size of a component. The default implementation calls getPreferredSize(javax.swing.JComponent), 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.

getMaximumSize

public Dimension getMaximumSize(JComponent c)
Determines the maximum size of a component. The default implementation calls getPreferredSize(javax.swing.JComponent), 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.

contains

public 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. 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

public static ComponentUI createUI(JComponent c)
Creates a delegate object for the specified component. Users should use the createUI method of a suitable subclass. The implementation of ComponentUI always throws an error.

Parameters:
c - the component for which a UI delegate is requested.

getAccessibleChildrenCount

public int getAccessibleChildrenCount(JComponent c)
Counts the number of accessible children in the component. The default implementation delegates the inquiry to the AccessibleContext of c.

Parameters:
c - the component whose accessible children are to be counted.

getAccessibleChild

public Accessible getAccessibleChild(JComponent c,
                                     int i)
Returns the specified accessible child of the component. The default implementation delegates the inquiry to the AccessibleContext of c.

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