    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}