001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.event;
018
019import java.util.EventObject;
020
021/**
022 * <p>
023 * The base class for all events generated by this library.
024 * </p>
025 * <p>
026 * The events produced by objects in this library are arranged in an inheritance
027 * hierarchy. This base class defines some basic properties common to all
028 * configuration events. Especially, an event has an {@link EventType} which
029 * describes its semantics. The event type can also be used for filtering for
030 * events or for defining event listeners on a fine-grained basis.
031 * </p>
032 *
033 * @version $Id: Event.java 1790899 2017-04-10 21:56:46Z ggregory $
034 * @since 2.0
035 */
036public class Event extends EventObject
037{
038    /**
039     * The root event type for all configuration-related events. All specific
040     * event types have this type as super direct (directly or indirectly).
041     */
042    public static final EventType<Event> ANY =
043            new EventType<>(null, "ANY");
044
045    /**
046     * Constant for the format used in toString() for a property representation.
047     */
048    private static final String FMT_PROPERTY = " %s=%s";
049
050    /**
051     * Constant for the initial buffer size for the generation of the string
052     * representation.
053     */
054    private static final int BUF_SIZE = 256;
055
056    /** The type of this event. */
057    private final EventType<? extends Event> eventType;
058
059    /**
060     * Creates a new instance of {@code Event} and sets basic properties.
061     *
062     * @param source the object on which the Event initially occurred (must not
063     *        be <b>null</b>)
064     * @param evType the type of this event (must not be <b>null</b>)
065     * @throws IllegalArgumentException if a required parameter is null
066     */
067    public Event(Object source, EventType<? extends Event> evType)
068    {
069        super(source);
070        if (evType == null)
071        {
072            throw new IllegalArgumentException("Event type must not be null!");
073        }
074        eventType = evType;
075    }
076
077    /**
078     * Returns the type of this event.
079     *
080     * @return the event type
081     */
082    public EventType<? extends Event> getEventType()
083    {
084        return eventType;
085    }
086
087    /**
088     * Returns a string representation for this object. This string contains the
089     * event class and a list of all properties.
090     *
091     * @return a string for this object
092     */
093    @Override
094    public String toString()
095    {
096        StringBuilder buf = new StringBuilder(BUF_SIZE);
097        buf.append(getClass().getSimpleName());
098        buf.append(" [");
099        appendPropertyRepresentation(buf, "source", getSource());
100        appendPropertyRepresentation(buf, "eventType", getEventType());
101        buf.append(" ]");
102        return buf.toString();
103    }
104
105    /**
106     * Helper method for appending a representation for a property to the
107     * overall string representation for this object. This method is called by
108     * {@code toString()} for generating string fragments for the properties of
109     * this class. It can also be used by derived classes which extend the
110     * string representation of this base class.
111     *
112     * @param buf the target buffer
113     * @param property the name of the property
114     * @param value the property value
115     */
116    protected void appendPropertyRepresentation(StringBuilder buf,
117            String property, Object value)
118    {
119        buf.append(String.format(FMT_PROPERTY, property, String.valueOf(value)));
120    }
121}