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.commons.collections.collection;
018    
019    import java.util.Collection;
020    import java.util.Iterator;
021    
022    import org.apache.commons.collections.Unmodifiable;
023    import org.apache.commons.collections.iterators.UnmodifiableIterator;
024    
025    /**
026     * Decorates another <code>Collection</code> to ensure it can't be altered.
027     * <p>
028     * This class is Serializable from Commons Collections 3.1.
029     *
030     * @since Commons Collections 3.0
031     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
032     * 
033     * @author Stephen Colebourne
034     */
035    public final class UnmodifiableCollection
036            extends AbstractSerializableCollectionDecorator
037            implements Unmodifiable {
038    
039        /** Serialization version */
040        private static final long serialVersionUID = -239892006883819945L;
041    
042        /**
043         * Factory method to create an unmodifiable collection.
044         * <p>
045         * If the collection passed in is already unmodifiable, it is returned.
046         * 
047         * @param coll  the collection to decorate, must not be null
048         * @return an unmodifiable collection
049         * @throws IllegalArgumentException if collection is null
050         */
051        public static Collection decorate(Collection coll) {
052            if (coll instanceof Unmodifiable) {
053                return coll;
054            }
055            return new UnmodifiableCollection(coll);
056        }
057        
058        //-----------------------------------------------------------------------
059        /**
060         * Constructor that wraps (not copies).
061         * 
062         * @param coll  the collection to decorate, must not be null
063         * @throws IllegalArgumentException if collection is null
064         */
065        private UnmodifiableCollection(Collection coll) {
066            super(coll);
067        }
068    
069        //-----------------------------------------------------------------------
070        public Iterator iterator() {
071            return UnmodifiableIterator.decorate(getCollection().iterator());
072        }
073    
074        public boolean add(Object object) {
075            throw new UnsupportedOperationException();
076        }
077    
078        public boolean addAll(Collection coll) {
079            throw new UnsupportedOperationException();
080        }
081    
082        public void clear() {
083            throw new UnsupportedOperationException();
084        }
085    
086        public boolean remove(Object object) {
087            throw new UnsupportedOperationException();
088        }
089    
090        public boolean removeAll(Collection coll) {
091            throw new UnsupportedOperationException();
092        }
093    
094        public boolean retainAll(Collection coll) {
095            throw new UnsupportedOperationException();
096        }
097    
098    }