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.xbean.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: 437551 $ $Date: 2006-08-28 06:14:47 +0000 (Mon, 28 Aug 2006) $
026     */
027    public final class UnionEnumeration implements Enumeration {
028        private final LinkedList enumerations = new LinkedList();
029    
030        public UnionEnumeration(List enumerations) {
031            this.enumerations.addAll(enumerations);
032        }
033    
034        public UnionEnumeration(Enumeration first, Enumeration 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 = (Enumeration) enumerations.getFirst();
045                if (enumeration.hasMoreElements()) {
046                    return true;
047                }
048                enumerations.removeFirst();
049            }
050            return false;
051        }
052    
053        public Object nextElement() {
054            while (!enumerations.isEmpty()) {
055                Enumeration enumeration = (Enumeration) enumerations.getFirst();
056                if (enumeration.hasMoreElements()) {
057                    return enumeration.nextElement();
058                }
059                enumerations.removeFirst();
060            }
061            throw new NoSuchElementException();
062        }
063    }