001/* VetoableChangeListener.java -- listen for a change which can be vetoed
002   Copyright (C) 1998, 2000, 2002 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
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013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
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017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.beans;
040
041import java.util.EventListener;
042
043/**
044 * VetoableChangeListener allows a class to monitor proposed changes to
045 * properties of a Bean and, if desired, prevent them from occurring. A
046 * vetoableChange() event will be fired <em>after</em> the property change has
047 * been requested, but before it is permanent. If any listener rejects the
048 * change by throwing the PropertyChangeException, a new vetoableChange()
049 * event will be fired to all listeners who received a vetoableChange() event
050 * in the first place, informing them to revert back to the old value. Thus,
051 * the listener that threw the exception the first time should be prepared
052 * to rethrow it the second time. The value, of course, never actually changed.
053 *
054 * <p><strong>Note:</strong> This class may not be reliably used to determine
055 * whether a property has actually changed.  Use the PropertyChangeListener
056 * interface for that instead.
057 *
058 * @author John Keiser
059 * @see java.beans.PropertyChangeListener
060 * @see java.beans.VetoableChangeSupport
061 * @since 1.1
062 * @status updated to 1.4
063 */
064public interface VetoableChangeListener extends EventListener
065{
066  /**
067   * Fired before a Bean's property changes.
068   *
069   * @param e the change (containing the old and new values)
070   * @throws PropertyVetoException if the change is vetoed by the listener
071   */
072  void vetoableChange(PropertyChangeEvent e) throws PropertyVetoException;
073} // interface VetoableChangeListener