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.xbean.classloader;
018
019import java.util.Enumeration;
020import java.util.LinkedList;
021import java.util.List;
022import java.util.NoSuchElementException;
023
024/**
025 * @version $Rev: 437551 $ $Date: 2006-08-28 08:14:47 +0200 (Mon, 28 Aug 2006) $
026 */
027public 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}