FileDocCategorySizeDatePackage
ComponentUI.javaAPI DocJava SE 6 API14341Tue Jun 10 00:26:44 BST 2008javax.swing.plaf

ComponentUI

public abstract class ComponentUI extends Object
The base class for all UI delegate objects in the Swing pluggable look and feel architecture. The UI delegate object for a Swing component is responsible for implementing the aspects of the component that depend on the look and feel. The JComponent class invokes methods from this class in order to delegate operations (painting, layout calculations, etc.) that may vary depending on the look and feel installed. Client programs should not invoke methods on this class directly.
see
javax.swing.JComponent
see
javax.swing.UIManager

Fields Summary
Constructors Summary
public ComponentUI()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

    
Methods Summary
public booleancontains(javax.swing.JComponent c, int x, int y)
Returns true if the specified x,y location is contained within the look and feel's defined shape of the specified component. x and y are defined to be relative to the coordinate system of the specified component. Although a component's bounds is constrained to a rectangle, this method provides the means for defining a non-rectangular shape within those bounds for the purpose of hit detection.

param
c the component where the x,y location is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
param
x the x coordinate of the point
param
y the y coordinate of the point
see
javax.swing.JComponent#contains
see
java.awt.Component#contains

	return c.inside(x, y);
    
public static javax.swing.plaf.ComponentUIcreateUI(javax.swing.JComponent c)
Returns an instance of the UI delegate for the specified component. Each subclass must provide its own static createUI method that returns an instance of that UI delegate subclass. If the UI delegate subclass is stateless, it may return an instance that is shared by multiple components. If the UI delegate is stateful, then it should return a new instance per component. The default implementation of this method throws an error, as it should never be invoked.

	throw new Error("ComponentUI.createUI not implemented.");
    
public javax.accessibility.AccessiblegetAccessibleChild(javax.swing.JComponent c, int i)
Returns the ith Accessible child of the object. UIs might need to override this if they present areas on the screen that can be viewed as components, but actual components are not used for presenting those areas.

Note: As of v1.3, it is recommended that developers call Component.AccessibleAWTComponent.getAccessibleChild() instead of this method.

see
#getAccessibleChildrenCount
param
i zero-based index of child
return
the ith Accessible child of the object

        return SwingUtilities.getAccessibleChild(c, i);
    
public intgetAccessibleChildrenCount(javax.swing.JComponent c)
Returns the number of accessible children in the object. If all of the children of this object implement Accessible, this method should return the number of children of this object. UIs might wish to override this if they present areas on the screen that can be viewed as components, but actual components are not used for presenting those areas. Note: As of v1.3, it is recommended that developers call Component.AccessibleAWTComponent.getAccessibleChildrenCount() instead of this method.

see
#getAccessibleChild
return
the number of accessible children in the object

        return SwingUtilities.getAccessibleChildrenCount(c);
    
public intgetBaseline(javax.swing.JComponent c, int width, int height)
Returns the baseline. The baseline is measured from the top of the component. This method is primarily meant for LayoutManagers to align components along their baseline. A return value less than 0 indicates this component does not have a reasonable baseline and that LayoutManagers should not align this component on its baseline.

This method returns -1. Subclasses that have a meaningful baseline should override appropriately.

param
c JComponent baseline is being requested for
param
width the width to get the baseline for
param
height the height to get the baseline for
throws
NullPointerException if c is null
throws
IllegalArgumentException if width or height is < 0
return
baseline or a value < 0 indicating there is no reasonable baseline
see
javax.swing.JComponent#getBaseline(int,int)
since
1.6

        if (c == null) {
            throw new NullPointerException("Component must be non-null");
        }
        if (width < 0 || height < 0) {
            throw new IllegalArgumentException(
                    "Width and height must be >= 0");
        }
        return -1;
    
public java.awt.Component$BaselineResizeBehaviorgetBaselineResizeBehavior(javax.swing.JComponent c)
Returns an enum indicating how the baseline of he component changes as the size changes. This method is primarily meant for layout managers and GUI builders.

This method returns BaselineResizeBehavior.OTHER. Subclasses that support a baseline should override appropriately.

param
c JComponent to return baseline resize behavior for
return
an enum indicating how the baseline changes as the component size changes
throws
NullPointerException if c is null
see
javax.swing.JComponent#getBaseline(int, int)
since
1.6

        if (c == null) {
            throw new NullPointerException("Component must be non-null");
        }
        return Component.BaselineResizeBehavior.OTHER;
    
public java.awt.DimensiongetMaximumSize(javax.swing.JComponent c)
Returns the specified component's maximum size appropriate for the look and feel. If null is returned, the maximum size will be calculated by the component's layout manager instead (this is the preferred approach for any component with a specific layout manager installed). The default implementation of this method invokes getPreferredSize and returns that value.

param
c the component whose maximum size is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
return
a Dimension object or null
see
javax.swing.JComponent#getMaximumSize
see
java.awt.LayoutManager2#maximumLayoutSize

	return getPreferredSize(c);
    
public java.awt.DimensiongetMinimumSize(javax.swing.JComponent c)
Returns the specified component's minimum size appropriate for the look and feel. If null is returned, the minimum size will be calculated by the component's layout manager instead (this is the preferred approach for any component with a specific layout manager installed). The default implementation of this method invokes getPreferredSize and returns that value.

param
c the component whose minimum size is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
return
a Dimension object or null
see
javax.swing.JComponent#getMinimumSize
see
java.awt.LayoutManager#minimumLayoutSize
see
#getPreferredSize

	return getPreferredSize(c);
    
public java.awt.DimensiongetPreferredSize(javax.swing.JComponent c)
Returns the specified component's preferred size appropriate for the look and feel. If null is returned, the preferred size will be calculated by the component's layout manager instead (this is the preferred approach for any component with a specific layout manager installed). The default implementation of this method returns null.

param
c the component whose preferred size is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
see
javax.swing.JComponent#getPreferredSize
see
java.awt.LayoutManager#preferredLayoutSize

	return null;
    
public voidinstallUI(javax.swing.JComponent c)
Configures the specified component appropriate for the look and feel. This method is invoked when the ComponentUI instance is being installed as the UI delegate on the specified component. This method should completely configure the component for the look and feel, including the following:
  1. Install any default property values for color, fonts, borders, icons, opacity, etc. on the component. Whenever possible, property values initialized by the client program should not be overridden.
  2. Install a LayoutManager on the component if necessary.
  3. Create/add any required sub-components to the component.
  4. Create/install event listeners on the component.
  5. Create/install a PropertyChangeListener on the component in order to detect and respond to component property changes appropriately.
  6. Install keyboard UI (mnemonics, traversal, etc.) on the component.
  7. Initialize any appropriate instance data.

param
c the component where this UI delegate is being installed
see
#uninstallUI
see
javax.swing.JComponent#setUI
see
javax.swing.JComponent#updateUI

    
public voidpaint(java.awt.Graphics g, javax.swing.JComponent c)
Paints the specified component appropriate for the look and feel. This method is invoked from the ComponentUI.update method when the specified component is being painted. Subclasses should override this method and use the specified Graphics object to render the content of the component.

param
g the Graphics context in which to paint
param
c the component being painted; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
see
#update

    
public voiduninstallUI(javax.swing.JComponent c)
Reverses configuration which was done on the specified component during installUI. This method is invoked when this UIComponent instance is being removed as the UI delegate for the specified component. This method should undo the configuration performed in installUI, being careful to leave the JComponent instance in a clean state (no extraneous listeners, look-and-feel-specific property objects, etc.). This should include the following:
  1. Remove any UI-set borders from the component.
  2. Remove any UI-set layout managers on the component.
  3. Remove any UI-added sub-components from the component.
  4. Remove any UI-added event/property listeners from the component.
  5. Remove any UI-installed keyboard UI from the component.
  6. Nullify any allocated instance data objects to allow for GC.

param
c the component from which this UI delegate is being removed; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
see
#installUI
see
javax.swing.JComponent#updateUI

    
public voidupdate(java.awt.Graphics g, javax.swing.JComponent c)
Notifies this UI delegate that it's time to paint the specified component. This method is invoked by JComponent when the specified component is being painted. By default this method will fill the specified component with its background color (if its opaque property is true) and then immediately call paint. In general this method need not be overridden by subclasses; all look-and-feel rendering code should reside in the paint method.

param
g the Graphics context in which to paint
param
c the component being painted; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
see
#paint
see
javax.swing.JComponent#paintComponent

	if (c.isOpaque()) {
	    g.setColor(c.getBackground());
	    g.fillRect(0, 0, c.getWidth(),c.getHeight());
	}
	paint(g, c);