    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}