1. /*

  2.  * @(#)UIResource.java	1.10 03/12/19

  3.  *

  4.  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.

  5.  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.

  6.  */

  7. 

  8. package javax.swing.plaf;

  9. 

  10. 

  11. /** 

  12.  * This interface is used to mark objects created by ComponentUI delegates.

  13.  * The <code>ComponentUI.installUI()</code> and 

  14.  * <code>ComponentUI.uninstallUI()</code> methods can use this interface

  15.  * to decide if a properties value has been overridden.  For example, the

  16.  * JList cellRenderer property is initialized by BasicListUI.installUI(),

  17.  * only if it's initial value is null:

  18.  * <pre>

  19.  * if (list.getCellRenderer() == null) {

  20.  *     list.setCellRenderer((ListCellRenderer)(UIManager.get("List.cellRenderer")));

  21.  * }

  22.  * </pre>

  23.  * At uninstallUI() time we reset the property to null if its value

  24.  * is an instance of UIResource:

  25.  * <pre>

  26.  * if (list.getCellRenderer() instanceof UIResource) {

  27.  *     list.setCellRenderer(null);

  28.  * }

  29.  *</pre>

  30.  * This pattern applies to all properties except the java.awt.Component

  31.  * properties font, foreground, and background.  If one of these

  32.  * properties isn't initialized, or is explicitly set to null, 

  33.  * its container provides the value.  For this reason the 

  34.  * <code>"== null"</code> is unreliable when installUI() is called

  35.  * to dynamically change a components look and feel.  So at installUI() 

  36.  * time we check to see if the current value is a UIResource:

  37.  *<pre>

  38.  * if (!(list.getFont() instanceof UIResource)) {

  39.  *     list.setFont(UIManager.getFont("List.font"));

  40.  * }

  41.  * </pre>

  42.  *

  43.  * @see ComponentUI

  44.  * @version 1.10 12/19/03

  45.  * @author Hans Muller

  46.  * 

  47.  */

  48. 

  49. public interface UIResource {

  50. }