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.set;
018
019import java.util.Collection;
020import java.util.Iterator;
021import java.util.Set;
022
023import org.apache.commons.collections4.Unmodifiable;
024import org.apache.commons.collections4.iterators.UnmodifiableIterator;
025
026/**
027 * Decorates another <code>Set</code> to ensure it can't be altered.
028 * <p>
029 * This class is Serializable from Commons Collections 3.1.
030 * <p>
031 * Attempts to modify it will result in an UnsupportedOperationException.
032 *
033 * @param <E> the type of the elements in this set
034 * @since 3.0
035 */
036public final class UnmodifiableSet<E>
037        extends AbstractSerializableSetDecorator<E>
038        implements Unmodifiable {
039
040    /** Serialization version */
041    private static final long serialVersionUID = 6499119872185240161L;
042
043    /**
044     * Factory method to create an unmodifiable set.
045     *
046     * @param <E> the element type
047     * @param set  the set to decorate, must not be null
048     * @return a new unmodifiable set
049     * @throws NullPointerException if set is null
050     * @since 4.0
051     */
052    public static <E> Set<E> unmodifiableSet(final Set<? extends E> set) {
053        if (set instanceof Unmodifiable) {
054            @SuppressWarnings("unchecked") // safe to upcast
055            final Set<E> tmpSet = (Set<E>) set;
056            return tmpSet;
057        }
058        return new UnmodifiableSet<>(set);
059    }
060
061    //-----------------------------------------------------------------------
062    /**
063     * Constructor that wraps (not copies).
064     *
065     * @param set  the set to decorate, must not be null
066     * @throws NullPointerException if set is null
067     */
068    @SuppressWarnings("unchecked") // safe to upcast
069    private UnmodifiableSet(final Set<? extends E> set) {
070        super((Set<E>) set);
071    }
072
073    //-----------------------------------------------------------------------
074    @Override
075    public Iterator<E> iterator() {
076        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
077    }
078
079    @Override
080    public boolean add(final E object) {
081        throw new UnsupportedOperationException();
082    }
083
084    @Override
085    public boolean addAll(final Collection<? extends E> coll) {
086        throw new UnsupportedOperationException();
087    }
088
089    @Override
090    public void clear() {
091        throw new UnsupportedOperationException();
092    }
093
094    @Override
095    public boolean remove(final Object object) {
096        throw new UnsupportedOperationException();
097    }
098
099    @Override
100    public boolean removeAll(final Collection<?> coll) {
101        throw new UnsupportedOperationException();
102    }
103
104    @Override
105    public boolean retainAll(final Collection<?> coll) {
106        throw new UnsupportedOperationException();
107    }
108
109}