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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package javax.swing.plaf;


This interface is used to mark objects created by ComponentUI delegates.
The ComponentUI.installUI() and
ComponentUI.uninstallUI() methods can use this interface
to decide if a properties value has been overridden.  For example, the
JList cellRenderer property is initialized by BasicListUI.installUI(),
only if it's initial value is null:
if (list.getCellRenderer() == null) {
    list.setCellRenderer((ListCellRenderer)(UIManager.get("List.cellRenderer")));
}

At uninstallUI() time we reset the property to null if its value
is an instance of UIResource:
if (list.getCellRenderer() instanceof UIResource) {
    list.setCellRenderer(null);
}

This pattern applies to all properties except the java.awt.Component
properties font, foreground, and background.  If one of these
properties isn't initialized, or is explicitly set to null,
its container provides the value.  For this reason the
"== null" is unreliable when installUI() is called
to dynamically change a components look and feel.  So at installUI()
time we check to see if the current value is a UIResource:
if (!(list.getFont() instanceof UIResource)) {
    list.setFont(UIManager.getFont("List.font"));
}

Author:
Hans Muller
See Also:
ComponentUI/**
 * This interface is used to mark objects created by ComponentUI delegates.
 * The <code>ComponentUI.installUI()</code> and
 * <code>ComponentUI.uninstallUI()</code> methods can use this interface
 * to decide if a properties value has been overridden.  For example, the
 * JList cellRenderer property is initialized by BasicListUI.installUI(),
 * only if it's initial value is null:
 * <pre>
 * if (list.getCellRenderer() == null) {
 *     list.setCellRenderer((ListCellRenderer)(UIManager.get("List.cellRenderer")));
 * }
 * </pre>
 * At uninstallUI() time we reset the property to null if its value
 * is an instance of UIResource:
 * <pre>
 * if (list.getCellRenderer() instanceof UIResource) {
 *     list.setCellRenderer(null);
 * }
 *</pre>
 * This pattern applies to all properties except the java.awt.Component
 * properties font, foreground, and background.  If one of these
 * properties isn't initialized, or is explicitly set to null,
 * its container provides the value.  For this reason the
 * <code>"== null"</code> is unreliable when installUI() is called
 * to dynamically change a components look and feel.  So at installUI()
 * time we check to see if the current value is a UIResource:
 *<pre>
 * if (!(list.getFont() instanceof UIResource)) {
 *     list.setFont(UIManager.getFont("List.font"));
 * }
 * </pre>
 *
 * @see ComponentUI
 * @author Hans Muller
 *
 */

public interface UIResource {
}