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.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 029 * type. The event type can be used to determine the meaning of a specific 030 * event. It also acts as filter criterion when event listeners are registered. 031 * The listener is then called only for events of this type or derived types. 032 * The events in this library form a natural hierarchy with base types and more 033 * specialized types. By specifying an appropriate event type at listener 034 * registration time, it can be determined on a fine-granular basis which events 035 * are propagated to the listener. 036 * </p> 037 * <p> 038 * Note: Users familiar with JavaFX probably recognize this approach to event 039 * handling. It allows for generic event listener interfaces and a natural 040 * selection of events to be processed. 041 * </p> 042 * 043 * @since 2.0 044 * @param <T> the event associated with this type 045 */ 046public class EventType<T extends Event> implements Serializable 047{ 048 /** Serial version UID. */ 049 private static final long serialVersionUID = 20150416L; 050 051 /** Constant for the format used by toString(). */ 052 private static final String FMT_TO_STRING = "%s [ %s ]"; 053 054 /** Stores the super type of this type. */ 055 private final EventType<? super T> superType; 056 057 /** A name for this event type. */ 058 private final String name; 059 060 /** 061 * Creates a new instance of {@code EventType} and initializes it with the 062 * super type and a type name. If no super type is specified, this is the 063 * root event type. 064 * 065 * @param superEventType the super event type 066 * @param typeName the name of this event type 067 */ 068 public EventType(final EventType<? super T> superEventType, final String typeName) 069 { 070 superType = superEventType; 071 name = typeName; 072 } 073 074 /** 075 * Returns the super event type. Result is <b>null</b> for the root event 076 * type. 077 * 078 * @return the super event type 079 */ 080 public EventType<? super T> getSuperType() 081 { 082 return superType; 083 } 084 085 /** 086 * Returns the name of this event type. The name has no specific semantic 087 * meaning. It is just used for debugging purposes and also part of the 088 * string representation of this event type. 089 * 090 * @return the event type name 091 */ 092 public String getName() 093 { 094 return name; 095 } 096 097 /** 098 * Returns a string representation for this object. This method is mainly 099 * overridden for debugging purposes. The returned string contains the name 100 * of this event type. 101 * 102 * @return a string for this object 103 */ 104 @Override 105 public String toString() 106 { 107 return String.format(FMT_TO_STRING, getClass().getSimpleName(), 108 getName()); 109 } 110 111 /** 112 * Returns a set with all event types that are super types of the specified 113 * type. This set contains the direct and indirect super types and also 114 * includes the given type itself. The passed in type may be <b>null</b>, 115 * then an empty set is returned. 116 * 117 * @param eventType the event type in question 118 * @return a set with all super event types 119 */ 120 public static Set<EventType<?>> fetchSuperEventTypes(final EventType<?> eventType) 121 { 122 final Set<EventType<?>> types = new HashSet<>(); 123 EventType<?> currentType = eventType; 124 while (currentType != null) 125 { 126 types.add(currentType); 127 currentType = currentType.getSuperType(); 128 } 129 return types; 130 } 131 132 /** 133 * Checks whether an event type is derived from another type. This 134 * implementation tests whether {@code baseType} is a direct or indirect 135 * super type of {@code derivedType}. If one of the types is <b>null</b>, 136 * result is <b>false</b>. 137 * 138 * @param derivedType the derived event type 139 * @param baseType the base event type 140 * @return <b>true</b> if the derived type is an instance of the base type, 141 * <b>false</b> otherwise 142 */ 143 public static boolean isInstanceOf(final EventType<?> derivedType, 144 final EventType<?> baseType) 145 { 146 EventType<?> currentType = derivedType; 147 while (currentType != null) 148 { 149 if (currentType == baseType) 150 { 151 return true; 152 } 153 currentType = currentType.getSuperType(); 154 } 155 return false; 156 } 157}