    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 *     https://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.io.Serializable;
    020import java.util.HashSet;
    021import java.util.Set;
    022
    023/**
    024 * <p>
    025 * A class representing an event type.
    026 * </p>
    027 * <p>
    028 * The events produced by <em>Commons Configuration</em> all have a specific type. The event type can be used to
    029 * determine the meaning of a specific event. It also acts as filter criterion when event listeners are registered. The
    030 * listener is then called only for events of this type or derived types. The events in this library form a natural
    031 * hierarchy with base types and more specialized types. By specifying an appropriate event type at listener
    032 * registration time, it can be determined on a fine-granular basis which events are propagated to the listener.
    033 * </p>
    034 * <p>
    035 * Note: Users familiar with JavaFX probably recognize this approach to event handling. It allows for generic event
    036 * listener interfaces and a natural selection of events to be processed.
    037 * </p>
    038 *
    039 * @param <T> the event associated with this type
    040 * @since 2.0
    041 */
    042public class EventType<T extends Event> implements Serializable {
    043
    044    /** Serial version UID. */
    045    private static final long serialVersionUID = 20150416L;
    046
    047    /** Constant for the format used by toString(). */
    048    private static final String FMT_TO_STRING = "%s [ %s ]";
    049
    050    /**
    051     * Returns a set with all event types that are super types of the specified type. This set contains the direct and
    052     * indirect super types and also includes the given type itself. The passed in type may be <strong>null</strong>, then an empty
    053     * set is returned.
    054     *
    055     * @param eventType the event type in question
    056     * @return a set with all super event types
    057     */
    058    public static Set<EventType<?>> fetchSuperEventTypes(final EventType<?> eventType) {
    059        final Set<EventType<?>> types = new HashSet<>();
    060        EventType<?> currentType = eventType;
    061        while (currentType != null) {
    062            types.add(currentType);
    063            currentType = currentType.getSuperType();
    064        }
    065        return types;
    066    }
    067
    068    /**
    069     * Checks whether an event type is derived from another type. This implementation tests whether {@code baseType} is a
    070     * direct or indirect super type of {@code derivedType}. If one of the types is <strong>null</strong>, result is <strong>false</strong>.
    071     *
    072     * @param derivedType the derived event type
    073     * @param baseType the base event type
    074     * @return <strong>true</strong> if the derived type is an instance of the base type, <strong>false</strong> otherwise
    075     */
    076    public static boolean isInstanceOf(final EventType<?> derivedType, final EventType<?> baseType) {
    077        EventType<?> currentType = derivedType;
    078        while (currentType != null) {
    079            if (currentType == baseType) {
    080                return true;
    081            }
    082            currentType = currentType.getSuperType();
    083        }
    084        return false;
    085    }
    086
    087    /** Stores the super type of this type. */
    088    private final EventType<? super T> superType;
    089
    090    /** A name for this event type. */
    091    private final String name;
    092
    093    /**
    094     * Creates a new instance of {@code EventType} and initializes it with the super type and a type name. If no super type
    095     * is specified, this is the root event type.
    096     *
    097     * @param superEventType the super event type
    098     * @param typeName the name of this event type
    099     */
    100    public EventType(final EventType<? super T> superEventType, final String typeName) {
    101        superType = superEventType;
    102        name = typeName;
    103    }
    104
    105    /**
    106     * Gets the name of this event type. The name has no specific semantic meaning. It is just used for debugging
    107     * purposes and also part of the string representation of this event type.
    108     *
    109     * @return the event type name
    110     */
    111    public String getName() {
    112        return name;
    113    }
    114
    115    /**
    116     * Gets the super event type. Result is <strong>null</strong> for the root event type.
    117     *
    118     * @return the super event type
    119     */
    120    public EventType<? super T> getSuperType() {
    121        return superType;
    122    }
    123
    124    /**
    125     * Returns a string representation for this object. This method is mainly overridden for debugging purposes. The
    126     * returned string contains the name of this event type.
    127     *
    128     * @return a string for this object
    129     */
    130    @Override
    131    public String toString() {
    132        return String.format(FMT_TO_STRING, getClass().getSimpleName(), getName());
    133    }
    134}