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;
021import java.util.function.Predicate;
022
023import org.apache.commons.collections4.Unmodifiable;
024import org.apache.commons.collections4.iterators.UnmodifiableIterator;
025
026/**
027 * Decorates another {@link Collection} to ensure it can't be altered.
028 * <p>
029 * This class is Serializable from Commons Collections 3.1.
030 * </p>
031 * <p>
032 * Attempts to modify it will result in an UnsupportedOperationException.
033 * </p>
034 *
035 * @param <E> the type of the elements in the collection
036 * @since 3.0
037 */
038public final class UnmodifiableCollection<E>
039        extends AbstractCollectionDecorator<E>
040        implements Unmodifiable {
041
042    /** Serialization version */
043    private static final long serialVersionUID = -239892006883819945L;
044
045    /**
046     * Factory method to create an unmodifiable collection.
047     * <p>
048     * If the collection passed in is already unmodifiable, it is returned.
049     *
050     * @param <T> the type of the elements in the collection
051     * @param coll  the collection to decorate, must not be null
052     * @return an unmodifiable collection
053     * @throws NullPointerException if collection is null
054     * @since 4.0
055     */
056    public static <T> Collection<T> unmodifiableCollection(final Collection<? extends T> coll) {
057        if (coll instanceof Unmodifiable) {
058            @SuppressWarnings("unchecked") // safe to upcast
059            final Collection<T> tmpColl = (Collection<T>) coll;
060            return tmpColl;
061        }
062        return new UnmodifiableCollection<>(coll);
063    }
064
065    //-----------------------------------------------------------------------
066    /**
067     * Constructor that wraps (not copies).
068     *
069     * @param coll  the collection to decorate, must not be null
070     * @throws NullPointerException if collection is null
071     */
072    @SuppressWarnings("unchecked") // safe to upcast
073    private UnmodifiableCollection(final Collection<? extends E> coll) {
074        super((Collection<E>) coll);
075    }
076
077    //-----------------------------------------------------------------------
078    @Override
079    public Iterator<E> iterator() {
080        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
081    }
082
083    @Override
084    public boolean add(final E object) {
085        throw new UnsupportedOperationException();
086    }
087
088    @Override
089    public boolean addAll(final Collection<? extends E> coll) {
090        throw new UnsupportedOperationException();
091    }
092
093    @Override
094    public void clear() {
095        throw new UnsupportedOperationException();
096    }
097
098    @Override
099    public boolean remove(final Object object) {
100        throw new UnsupportedOperationException();
101    }
102
103    /**
104     * @since 4.4
105     */
106    @Override
107    public boolean removeIf(final Predicate<? super E> filter) {
108        throw new UnsupportedOperationException();
109    }
110
111    @Override
112    public boolean removeAll(final Collection<?> coll) {
113        throw new UnsupportedOperationException();
114    }
115
116    @Override
117    public boolean retainAll(final Collection<?> coll) {
118        throw new UnsupportedOperationException();
119    }
120
121}