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 */ 017 018package org.apache.commons.net.util; 019 020import java.io.ObjectInputStream; 021import java.io.ObjectOutputStream; 022import java.io.Serializable; 023import java.util.EventListener; 024import java.util.Iterator; 025import java.util.concurrent.CopyOnWriteArrayList; 026 027/** 028 * A list of event listeners. 029 * 030 * @param <T> the type of elements returned by the iterator 031 */ 032public class ListenerList<T extends EventListener> implements Serializable, Iterable<T> { 033 034 private static final long serialVersionUID = -1934227607974228213L; 035 036 /** 037 * The thread-safe list of listeners. 038 */ 039 private final CopyOnWriteArrayList<T> listeners; 040 041 /** 042 * Constructs a new instance. 043 */ 044 public ListenerList() { 045 listeners = new CopyOnWriteArrayList<>(); 046 } 047 048 /** 049 * Adds the given listener to the end of this list. 050 * 051 * @param listener A listener. 052 */ 053 public void addListener(final T listener) { 054 listeners.add(listener); 055 } 056 057 /** 058 * Gets the number of elements in this list. 059 * 060 * @return the number of elements in this list 061 */ 062 public int getListenerCount() { 063 return listeners.size(); 064 } 065 066 /** 067 * Tests whether if this listener list is empty. 068 * 069 * @return whether if this listener list is empty. 070 * @since 3.12.0 071 */ 072 public boolean isEmpty() { 073 return getListenerCount() == 0; 074 } 075 076 /** 077 * Return an {@link Iterator} for the {@link EventListener} instances. 078 * 079 * @return an {@link Iterator} for the {@link EventListener} instances 080 * @since 2.0 TODO Check that this is a good defensive strategy 081 */ 082 @Override 083 public Iterator<T> iterator() { 084 return listeners.iterator(); 085 } 086 087 /** 088 * Throws UnsupportedOperationException. 089 * 090 * @param ignored Ignore. 091 */ 092 private void readObject(final ObjectInputStream ignored) { 093 throw new UnsupportedOperationException("Serialization is not supported"); 094 } 095 096 /** 097 * Removes the first occurrence of the specified listener from this list, if it is present. 098 * 099 * @param listener listener to be removed from this list, if present. 100 */ 101 public void removeListener(final T listener) { 102 listeners.remove(listener); 103 } 104 105 /** 106 * Always throws {@link UnsupportedOperationException}. 107 * 108 * @param ignored ignored. 109 * @throws UnsupportedOperationException Always thrown. 110 */ 111 private void writeObject(final ObjectOutputStream ignored) { 112 throw new UnsupportedOperationException("Serialization is not supported"); 113 } 114 115}