gcc/libjava/java/beans/PropertyChangeEvent.java

/* PropertyChangeEvent.java -- describes a change in a property
   Copyright (C) 1998, 2000, 2002 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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GNU Classpath 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 for more details.

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02111-1307 USA.

Linking this library statically or dynamically with other modules is
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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exception statement from your version. */


package java.beans;

import java.util.EventObject;

/**
 * PropertyChangeEvents are fired in the PropertyChange and VetoableChange
 * event classes.  They represent the old and new values as well as the
 * source Bean. If the old or new value is a primitive type, it must be
 * wrapped in the appropriate wrapper type (java.lang.Integer for int, etc.,
 * etc.).
 *
 * <p>If the old or new values are unknown (although why that would be I do
 * not know), they may be null. Also, if the set of properties itself has
 * changed, the name should be null, and the old and new values may also be
 * null. Right now Sun put in a propagationId, reserved for future use. Read
 * the comments on the constructor and on setPropagationId for more
 * information.
 *
 * @author John Keiser
 * @author Eric Blake <ebb9@email.byu.edu>
 * @since 1.1
 * @status udpated to 1.4
 */
public class PropertyChangeEvent extends EventObject
{
  /**
   * Compatible with JDK 1.1+.
   */
  private static final long serialVersionUID = 7042693688939648123L;

  /**
   * The name of the property that changed, may be null. Package visible for
   * use by PropertyChangeSupport.
   *
   * @serial the changed property name
   */
  final String propertyName;

  /**
   * The new value of the property, may be null. Package visible for use by
   * PropertyChangeSupport.
   *
   * @serial the new property value
   */
  final Object newValue;

  /**
   * The old value of the property, may be null. Package visible for use by
   * PropertyChangeSupport.
   *
   * @serial the old property value
   */
  final Object oldValue;

  /**
   * The propagation ID, reserved for future use. May be null.
   *
   * @see #getPropagationId()
   * @serial the Propagation ID
   */
  private Object propagationId;

  /**
   * Create a new PropertyChangeEvent. Remember that if you received a
   * PropertyChangeEvent and are sending a new one, you should also set the
   * propagation ID from the old PropertyChangeEvent.
   *
   * @param source the Bean containing the property
   * @param propertyName the property's name
   * @param oldValue the old value of the property
   * @param newValue the new value of the property
   * @throws IllegalArgumentException if source is null
   */
  public PropertyChangeEvent(Object source, String propertyName,
                             Object oldVal, Object newVal)
  {
    super(source);
    this.propertyName = propertyName;
    oldValue = oldVal;
    newValue = newVal;
  }

  /**
   * Get the property name. May be null if multiple properties changed.
   *
   * @return the property name
   */
  public String getPropertyName()
  {
    return propertyName;
  }

  /**
   * Get the property's new value. May be null if multiple properties changed.
   *
   * @return the property's new value
   */
  public Object getNewValue()
  {
    return newValue;
  }

  /**
   * Get the property's old value. May be null if multiple properties changed.
   *
   * @return the property's old value
   */
  public Object getOldValue()
  {
    return oldValue;
  }

  /**
   * Set the propagation ID.  This is a way for the event to be passed from
   * hand to hand and retain a little extra state.  Right now it is unused,
   * but it should be propagated anyway so that future versions of JavaBeans
   * can use it, for God knows what.
   *
   * @param propagationId the propagation ID
   * @see #getPropagationId()
   */
  public void setPropagationId(Object propagationId)
  {
    this.propagationId = propagationId;
  }

  /**
   * Get the propagation ID. Right now, it is not used for anything.
   *
   * @return the propagation ID
   * @see #setPropagationId(Object)
   */
  public Object getPropagationId()
  {
    return propagationId;
  }

  /**
   * Utility method to rollback a change.
   *
   * @param event the event to rollback
   * @return a new event with old and new swapped
   */
  PropertyChangeEvent rollback()
  {
    PropertyChangeEvent result
      = new PropertyChangeEvent(source, propertyName, newValue, oldValue);
    result.propagationId = propagationId;
    return result;
  }
} // class PropertyChangeEvent