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     */
017    package org.apache.geronimo.kernel.classloader;
018    
019    import java.util.Enumeration;
020    import java.util.LinkedList;
021    import java.util.List;
022    import java.util.NoSuchElementException;
023    
024    /**
025     * @version $Rev: 706640 $ $Date: 2008-10-21 14:44:05 +0000 (Tue, 21 Oct 2008) $
026     */
027    public final class UnionEnumeration<T> implements Enumeration<T> {
028        private final LinkedList<Enumeration<T>> enumerations = new LinkedList<Enumeration<T>>();
029    
030        public UnionEnumeration(List<Enumeration<T>> enumerations) {
031            this.enumerations.addAll(enumerations);
032        }
033    
034        public UnionEnumeration(Enumeration<T> first, Enumeration<T> second) {
035            if (first == null) throw new NullPointerException("first is null");
036            if (second == null) throw new NullPointerException("second is null");
037    
038            enumerations.add(first);
039            enumerations.add(second);
040        }
041    
042        public boolean hasMoreElements() {
043            while (!enumerations.isEmpty()) {
044                Enumeration enumeration = enumerations.getFirst();
045                if (enumeration.hasMoreElements()) {
046                    return true;
047                }
048                enumerations.removeFirst();
049            }
050            return false;
051        }
052    
053        public T nextElement() {
054            while (!enumerations.isEmpty()) {
055                Enumeration<T> enumeration = enumerations.getFirst();
056                if (enumeration.hasMoreElements()) {
057                    return enumeration.nextElement();
058                }
059                enumerations.removeFirst();
060            }
061            throw new NoSuchElementException();
062        }
063    }