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.commons.collections4.collection;
018
019import java.util.Collection;
020import java.util.Iterator;
021
022import org.apache.commons.collections4.Unmodifiable;
023import org.apache.commons.collections4.iterators.UnmodifiableIterator;
024
025/**
026 * Decorates another {@link Collection} to ensure it can't be altered.
027 * <p>
028 * This class is Serializable from Commons Collections 3.1.
029 * <p>
030 * Attempts to modify it will result in an UnsupportedOperationException.
031 *
032 * @param <E> the type of the elements in the collection
033 * @since 3.0
034 * @version $Id: UnmodifiableCollection.html 972421 2015-11-14 20:00:04Z tn $
035 */
036public final class UnmodifiableCollection<E>
037        extends AbstractCollectionDecorator<E>
038        implements Unmodifiable {
039
040    /** Serialization version */
041    private static final long serialVersionUID = -239892006883819945L;
042
043    /**
044     * Factory method to create an unmodifiable collection.
045     * <p>
046     * If the collection passed in is already unmodifiable, it is returned.
047     *
048     * @param <T> the type of the elements in the collection
049     * @param coll  the collection to decorate, must not be null
050     * @return an unmodifiable collection
051     * @throws IllegalArgumentException if collection is null
052     * @since 4.0
053     */
054    public static <T> Collection<T> unmodifiableCollection(final Collection<? extends T> coll) {
055        if (coll instanceof Unmodifiable) {
056            @SuppressWarnings("unchecked") // safe to upcast
057            final Collection<T> tmpColl = (Collection<T>) coll;
058            return tmpColl;
059        }
060        return new UnmodifiableCollection<T>(coll);
061    }
062
063    //-----------------------------------------------------------------------
064    /**
065     * Constructor that wraps (not copies).
066     *
067     * @param coll  the collection to decorate, must not be null
068     * @throws IllegalArgumentException if collection is null
069     */
070    @SuppressWarnings("unchecked") // safe to upcast
071    private UnmodifiableCollection(final Collection<? extends E> coll) {
072        super((Collection<E>) coll);
073    }
074
075    //-----------------------------------------------------------------------
076    @Override
077    public Iterator<E> iterator() {
078        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
079    }
080
081    @Override
082    public boolean add(final E object) {
083        throw new UnsupportedOperationException();
084    }
085
086    @Override
087    public boolean addAll(final Collection<? extends E> coll) {
088        throw new UnsupportedOperationException();
089    }
090
091    @Override
092    public void clear() {
093        throw new UnsupportedOperationException();
094    }
095
096    @Override
097    public boolean remove(final Object object) {
098        throw new UnsupportedOperationException();
099    }
100
101    @Override
102    public boolean removeAll(final Collection<?> coll) {
103        throw new UnsupportedOperationException();
104    }
105
106    @Override
107    public boolean retainAll(final Collection<?> coll) {
108        throw new UnsupportedOperationException();
109    }
110
111}