27.4 Rendering Odds and Ends

Both the JTree and JTable classes make use of cell renderers to display cells and cell editors to modify cell values. The following classes round out the utilities available for rendering information.

27.4.1 The CellRendererPane Class

This utility class was built to keep renderers from propagating repaint( ) and validate( ) calls to the components using renderer components such as JTree and JList. If you played around with creating your own renderers for any of the Swing components that use them, you'll recall that you did not use this class yourself. Normally this pane is wrapped around the renderer and the various paintComponent( ) methods below are used to do the actual drawing. Developers do not normally need to worry about this class.

27.4.2 The Renderer Interface

The Swing package includes a Renderer interface (which does not appear to be used within Swing itself) with the following methods:

public Component getComponent( )

Return a Component you can use with something like the SwingUtilities.paintComponent( ) method to draw the value on the screen.

public void setValue(Object aValue, boolean isSelected)

This method can initialize the rendering component to reflect the state of the object aValue.

This interface could be useful if you were to create a library of renderers for use with your own applications; however, it is not implemented anywhere in the Swing package as of SDK 1.4.1.

27.4.3 The GrayFilter Class

The GrayFilter class is an extension of the java.awt.image.RGBImageFilter class. This class contains a static method that returns a "disabled" version of an image passed in. The image is converted to a grayscale version, and some lighter parts of the image are amplified to ensure the image is recognizable. All of the components that can display images use this class to present a default disabled version of the image if an explicit disabled image is not provided.

If you want the gory details on image manipulation with Java 2, check out Java 2D Graphics by Jonathan Knudsen (O'Reilly & Associates).

27.4.3.1 Constructor

public GrayFilter(boolean brighter, int percent)

Create an instance of the GrayFilter class that you can use to do your own filtering. (Normally you don't call this, but use createDisabledImage( ) instead.) Both the brighter and percent arguments are used to convert color pixels to appropriately shaded gray pixels.

27.4.3.2 Image methods

public static Image createDisabledImage(Image i)

Use this method to retrieve a grayed-out version of the image i. This method creates an instance of the GrayFilter class with brighter turned on and a gray percent of 50.

public int filterRGB(int x, int y, int rgb)

Override the filterRGB( ) method in RGBImageFilter, convert the rgb pixel to a gray pixel, and return that.