View Javadoc
1   /*
2    * Copyright (c) 1997, 1998, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package javax.swing.plaf;
27  
28  
29  /**
30   * This interface is used to mark objects created by ComponentUI delegates.
31   * The <code>ComponentUI.installUI()</code> and
32   * <code>ComponentUI.uninstallUI()</code> methods can use this interface
33   * to decide if a properties value has been overridden.  For example, the
34   * JList cellRenderer property is initialized by BasicListUI.installUI(),
35   * only if it's initial value is null:
36   * <pre>
37   * if (list.getCellRenderer() == null) {
38   *     list.setCellRenderer((ListCellRenderer)(UIManager.get("List.cellRenderer")));
39   * }
40   * </pre>
41   * At uninstallUI() time we reset the property to null if its value
42   * is an instance of UIResource:
43   * <pre>
44   * if (list.getCellRenderer() instanceof UIResource) {
45   *     list.setCellRenderer(null);
46   * }
47   *</pre>
48   * This pattern applies to all properties except the java.awt.Component
49   * properties font, foreground, and background.  If one of these
50   * properties isn't initialized, or is explicitly set to null,
51   * its container provides the value.  For this reason the
52   * <code>"== null"</code> is unreliable when installUI() is called
53   * to dynamically change a components look and feel.  So at installUI()
54   * time we check to see if the current value is a UIResource:
55   *<pre>
56   * if (!(list.getFont() instanceof UIResource)) {
57   *     list.setFont(UIManager.getFont("List.font"));
58   * }
59   * </pre>
60   *
61   * @see ComponentUI
62   * @author Hans Muller
63   *
64   */
65  
66  public interface UIResource {
67  }