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 */
035public final class UnmodifiableCollection<E>
036        extends AbstractCollectionDecorator<E>
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 <T> the type of the elements in the collection
048     * @param coll  the collection to decorate, must not be null
049     * @return an unmodifiable collection
050     * @throws NullPointerException if collection is null
051     * @since 4.0
052     */
053    public static <T> Collection<T> unmodifiableCollection(final Collection<? extends T> coll) {
054        if (coll instanceof Unmodifiable) {
055            @SuppressWarnings("unchecked") // safe to upcast
056            final Collection<T> tmpColl = (Collection<T>) coll;
057            return tmpColl;
058        }
059        return new UnmodifiableCollection<>(coll);
060    }
061
062    //-----------------------------------------------------------------------
063    /**
064     * Constructor that wraps (not copies).
065     *
066     * @param coll  the collection to decorate, must not be null
067     * @throws NullPointerException if collection is null
068     */
069    @SuppressWarnings("unchecked") // safe to upcast
070    private UnmodifiableCollection(final Collection<? extends E> coll) {
071        super((Collection<E>) coll);
072    }
073
074    //-----------------------------------------------------------------------
075    @Override
076    public Iterator<E> iterator() {
077        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
078    }
079
080    @Override
081    public boolean add(final E object) {
082        throw new UnsupportedOperationException();
083    }
084
085    @Override
086    public boolean addAll(final Collection<? extends E> coll) {
087        throw new UnsupportedOperationException();
088    }
089
090    @Override
091    public void clear() {
092        throw new UnsupportedOperationException();
093    }
094
095    @Override
096    public boolean remove(final Object object) {
097        throw new UnsupportedOperationException();
098    }
099
100    @Override
101    public boolean removeAll(final Collection<?> coll) {
102        throw new UnsupportedOperationException();
103    }
104
105    @Override
106    public boolean retainAll(final Collection<?> coll) {
107        throw new UnsupportedOperationException();
108    }
109
110}