1 /*
2 * Copyright 1997-1998 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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 }
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