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Tools to assist in the reading of configuration/preferences files in various formats
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration.event;

import java.util.EventObject;

/**
 * 
 * An event class for reporting updates on a configuration object.
 * 
 * 
 * Event objects of this type are used for "raw" events, i.e.
 * unfiltered modifications of any kind. A level with semantically higher events
 * (e.g. for property changes) may be built on top of this fundamental event
 * mechanism.
 * 
 * 
 * Each event can contain the following data:
 * 

 * A source object, which is usually the configuration object that was
 * modified.
 * The event's type. This is a numeric value that corresponds to constant
 * declarations in concrete configuration classes. It describes what exactly has
 * happended.
 * If available, the name of the property whose modification caused the
 * event.
 * If available, the value of the property that caused this event.
 * A flag whether this event was generated before or after the update of
 * the source configuration. A modification of a configuration typically causes
 * two events: one event before and one event after the modification is
 * performed. This allows event listeners to react at the correct point of time.
 * 
 * 
 * 
 * The following standard events are generated by typical configuration
 * implementations (the constants for the event types are defined in
 * {@link org.apache.commons.configuration.AbstractConfiguration}):
 * 

 * EVENT_ADD_PROPERTY
 * This event is triggered for each call of the addProperty()
 * method of a configuration object. It contains the name of the property, to
 * which new data is added, and the value object that is added to this property
 * (this may be an array or a list if multiple values are added).
 * EVENT_SET_PROPERTY
 * Calling the setProperty() method triggers this event. The
 * event object stores the name of the affected property and its new value.
 * EVENT_CLEAR_PROPERTY
 * If a property is removed from a configuration (by calling the
 * clearProperty() method), an event of this type is fired. In
 * this case the event object only stores the name of the removed property, the
 * value is null.
 * EVENT_CLEAR
 * This event is fired when the whole configuration is cleared. The
 * corresponding event object contains no additional data.
 * 
 * 
 *
 * @author Commons
 * Configuration team
 * @version $Id: ConfigurationEvent.java 561230 2007-07-31 04:17:09Z rahul $
 * @since 1.3
 */
public class ConfigurationEvent extends EventObject
{
    /**
     * The serial version UID.
     */
    private static final long serialVersionUID = 3277238219073504136L;

    /** Stores the event type. */
    private int type;

    /** Stores the property name. */
    private String propertyName;

    /** Stores the property value. */
    private Object propertyValue;

    /** Stores the before update flag. */
    private boolean beforeUpdate;

    /**
     * Creates a new instance of ConfigurationEvent and
     * initializes it.
     *
     * @param source the event source
     * @param type the event's type
     * @param propertyName the name of the affected property
     * @param propertyValue the value of the affected property
     * @param beforeUpdate the before update flag
     */
    public ConfigurationEvent(Object source, int type, String propertyName,
            Object propertyValue, boolean beforeUpdate)
    {
        super(source);
        this.type = type;
        this.propertyName = propertyName;
        this.propertyValue = propertyValue;
        this.beforeUpdate = beforeUpdate;
    }

    /**
     * Returns the name of the affected property. This can be null if no
     * property change has lead to this event.
     *
     * @return the name of the property
     */
    public String getPropertyName()
    {
        return propertyName;
    }

    /**
     * Returns the value of the affected property if available.
     *
     * @return the value of the property; can be null
     */
    public Object getPropertyValue()
    {
        return propertyValue;
    }

    /**
     * Returns the type of this event. This describes the update process that
     * caused this event.
     *
     * @return the event's type
     */
    public int getType()
    {
        return type;
    }

    /**
     * Returns a flag if this event was generated before or after an update.
     *
     * @return true if this event was generated before an update;
     * false otherwise
     */
    public boolean isBeforeUpdate()
    {
        return beforeUpdate;
    }
}