JDK8/Java8源码在线阅读

/*
 * Copyright (c) 1996, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.beans;

import java.util.EventObject;

/**
 * A "PropertyChange" event gets delivered whenever a bean changes a "bound"
 * or "constrained" property.  A PropertyChangeEvent object is sent as an
 * argument to the PropertyChangeListener and VetoableChangeListener methods.
 * <P>
 * Normally PropertyChangeEvents are accompanied by the name and the old
 * and new value of the changed property.  If the new value is a primitive
 * type (such as int or boolean) it must be wrapped as the
 * corresponding java.lang.* Object type (such as Integer or Boolean).
 * <P>
 * Null values may be provided for the old and the new values if their
 * true values are not known.
 * <P>
 * An event source may send a null object as the name to indicate that an
 * arbitrary set of if its properties have changed.  In this case the
 * old and new values should also be null.
 */
public class PropertyChangeEvent extends EventObject {
    private static final long serialVersionUID = 7042693688939648123L;

    /**
     * Constructs a new {@code PropertyChangeEvent}.
     *
     * @param source        the bean that fired the event
     * @param propertyName  the programmatic name of the property that was changed
     * @param oldValue      the old value of the property
     * @param newValue      the new value of the property
     *
     * @throws IllegalArgumentException if {@code source} is {@code null}
     */
    public PropertyChangeEvent(Object source, String propertyName,
                               Object oldValue, Object newValue) {
        super(source);
        this.propertyName = propertyName;
        this.newValue = newValue;
        this.oldValue = oldValue;
    }

    /**
     * Gets the programmatic name of the property that was changed.
     *
     * @return  The programmatic name of the property that was changed.
     *          May be null if multiple properties have changed.
     */
    public String getPropertyName() {
        return propertyName;
    }

    /**
     * Gets the new value for the property, expressed as an Object.
     *
     * @return  The new value for the property, expressed as an Object.
     *          May be null if multiple properties have changed.
     */
    public Object getNewValue() {
        return newValue;
    }

    /**
     * Gets the old value for the property, expressed as an Object.
     *
     * @return  The old value for the property, expressed as an Object.
     *          May be null if multiple properties have changed.
     */
    public Object getOldValue() {
        return oldValue;
    }

    /**
     * Sets the propagationId object for the event.
     *
     * @param propagationId  The propagationId object for the event.
     */
    public void setPropagationId(Object propagationId) {
        this.propagationId = propagationId;
    }

    /**
     * The "propagationId" field is reserved for future use.  In Beans 1.0
     * the sole requirement is that if a listener catches a PropertyChangeEvent
     * and then fires a PropertyChangeEvent of its own, then it should
     * make sure that it propagates the propagationId field from its
     * incoming event to its outgoing event.
     *
     * @return the propagationId object associated with a bound/constrained
     *          property update.
     */
    public Object getPropagationId() {
        return propagationId;
    }

    /**
     * name of the property that changed.  May be null, if not known.
     * @serial
     */
    private String propertyName;

    /**
     * New value for property.  May be null if not known.
     * @serial
     */
    private Object newValue;

    /**
     * Previous value for property.  May be null if not known.
     * @serial
     */
    private Object oldValue;

    /**
     * Propagation ID.  May be null.
     * @serial
     * @see #getPropagationId
     */
    private Object propagationId;

    /**
     * Returns a string representation of the object.
     *

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