package org.eclipse.jface.util;

/*
 * (c) Copyright IBM Corp. 2000, 2001.
 * All Rights Reserved.
 */
import java.util.EventObject;

/**
 * An event object describing a change to a named property.
 * <p>
 * This concrete class was designed to be instantiated, but may
 * also be subclassed if required.
 * </p>
 * <p>
 * The JFace frameworks contain classes that report property 
 * change events for internal state changes that may be of interest
 * to external parties. A special listener interface
 * (<code>IPropertyChangeListener</code>) is defined for this purpose,
 * and a typical class allow listeners to be registered via
 * an <code>addPropertyChangeListener</code> method.
 * </p>
 *
 * @see IPropertyChangeListener
 */
public class PropertyChangeEvent extends EventObject {

	/**
	 * The name of the changed property.
	 */
	private String propertyName;

	/**
	 * The old value of the changed property, or <code>null</code> if
	 * not known or not relevant.
	 */
	private Object oldValue;

	/**
	 * The new value of the changed property, or <code>null</code> if
	 * not known or not relevant.
	 */
	private Object newValue;
/**
 * Creates a new property change event.
 *
 * @param source the object whose property has changed
 * @param property the property that has changed (must not be <code>null</code>)
 * @param oldValue the old value of the property, or <code>null</code> if none
 * @param newValue the new value of the property, or <code>null</code> if none
 */
public PropertyChangeEvent(Object source, String property, Object oldValue, Object newValue) {
	super(source);
	Assert.isNotNull(property);
	this.propertyName = property;
	this.oldValue = oldValue;
	this.newValue = newValue;
}
/**
 * Returns the new value of the property.
 *
 * @return the new value, or <code>null</code> if not known
 *  or not relevant
 */
public Object getNewValue() {
	return newValue;
}
/**
 * Returns the old value of the property.
 *
 * @return the old value, or <code>null</code> if not known
 *  or not relevant
 */
public Object getOldValue() {
	return oldValue;
}
/**
 * Returns the name of the property that changed.
 * <p>
 * Warning: there is no guarantee that the property name returned
 * is a constant string.  Callers must compare property names using
 * equals, not ==.
 * </p>
 *
 * @return the name of the property that changed
 */
public String getProperty() {
	return propertyName;
}
}