1. /*

  2.  * @(#)UIResource.java	1.7 00/02/02

  3.  *

  4.  * Copyright 1997-2000 Sun Microsystems, Inc. All Rights Reserved.

  5.  * 

  6.  * This software is the proprietary information of Sun Microsystems, Inc.  

  7.  * Use is subject to license terms.

  8.  * 

  9.  */

  10. 

  11. package javax.swing.plaf;

  12. 

  13. 

  14. /** 

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

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

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

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

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

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

  21.  * <pre>

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

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

  24.  * }

  25.  * </pre>

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

  27.  * is an instance of UIResource:

  28.  * <pre>

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

  30.  *     list.setCellRenderer(null);

  31.  * }

  32.  *</pre>

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

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

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

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

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

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

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

  40.  *<pre>

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

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

  43.  * }

  44.  * </pre>

  45.  *

  46.  * @see ComponentUI

  47.  * @version 1.7 02/02/00

  48.  * @author Hans Muller

  49.  * 

  50.  */

  51. 

  52. public interface UIResource {

  53. }