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 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 * @since 2.0 040 * @param <T> the event associated with this type 041 */ 042public class EventType<T extends Event> implements Serializable { 043 /** Serial version UID. */ 044 private static final long serialVersionUID = 20150416L; 045 046 /** Constant for the format used by toString(). */ 047 private static final String FMT_TO_STRING = "%s [ %s ]"; 048 049 /** Stores the super type of this type. */ 050 private final EventType<? super T> superType; 051 052 /** A name for this event type. */ 053 private final String name; 054 055 /** 056 * Creates a new instance of {@code EventType} and initializes it with the super type and a type name. If no super type 057 * is specified, this is the root event type. 058 * 059 * @param superEventType the super event type 060 * @param typeName the name of this event type 061 */ 062 public EventType(final EventType<? super T> superEventType, final String typeName) { 063 superType = superEventType; 064 name = typeName; 065 } 066 067 /** 068 * Gets the super event type. Result is <b>null</b> for the root event type. 069 * 070 * @return the super event type 071 */ 072 public EventType<? super T> getSuperType() { 073 return superType; 074 } 075 076 /** 077 * Gets the name of this event type. The name has no specific semantic meaning. It is just used for debugging 078 * purposes and also part of the string representation of this event type. 079 * 080 * @return the event type name 081 */ 082 public String getName() { 083 return name; 084 } 085 086 /** 087 * Returns a string representation for this object. This method is mainly overridden for debugging purposes. The 088 * returned string contains the name of this event type. 089 * 090 * @return a string for this object 091 */ 092 @Override 093 public String toString() { 094 return String.format(FMT_TO_STRING, getClass().getSimpleName(), getName()); 095 } 096 097 /** 098 * Returns a set with all event types that are super types of the specified type. This set contains the direct and 099 * indirect super types and also includes the given type itself. The passed in type may be <b>null</b>, then an empty 100 * set is returned. 101 * 102 * @param eventType the event type in question 103 * @return a set with all super event types 104 */ 105 public static Set<EventType<?>> fetchSuperEventTypes(final EventType<?> eventType) { 106 final Set<EventType<?>> types = new HashSet<>(); 107 EventType<?> currentType = eventType; 108 while (currentType != null) { 109 types.add(currentType); 110 currentType = currentType.getSuperType(); 111 } 112 return types; 113 } 114 115 /** 116 * Checks whether an event type is derived from another type. This implementation tests whether {@code baseType} is a 117 * direct or indirect super type of {@code derivedType}. If one of the types is <b>null</b>, result is <b>false</b>. 118 * 119 * @param derivedType the derived event type 120 * @param baseType the base event type 121 * @return <b>true</b> if the derived type is an instance of the base type, <b>false</b> otherwise 122 */ 123 public static boolean isInstanceOf(final EventType<?> derivedType, final EventType<?> baseType) { 124 EventType<?> currentType = derivedType; 125 while (currentType != null) { 126 if (currentType == baseType) { 127 return true; 128 } 129 currentType = currentType.getSuperType(); 130 } 131 return false; 132 } 133}