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;
022import java.util.function.Predicate;
023
024import org.apache.commons.collections4.Unmodifiable;
025import org.apache.commons.collections4.iterators.UnmodifiableIterator;
026
027/**
028 * Decorates another {@code Set} to ensure it can't be altered.
029 * <p>
030 * This class is Serializable from Commons Collections 3.1.
031 * </p>
032 * <p>
033 * Attempts to modify it will result in an UnsupportedOperationException.
034 * </p>
035 *
036 * @param <E> the type of the elements in this set
037 * @since 3.0
038 */
039public final class UnmodifiableSet<E>
040        extends AbstractSerializableSetDecorator<E>
041        implements Unmodifiable {
042
043    /** Serialization version */
044    private static final long serialVersionUID = 6499119872185240161L;
045
046    /**
047     * Factory method to create an unmodifiable set.
048     *
049     * @param <E> the element type
050     * @param set  the set to decorate, must not be null
051     * @return a new unmodifiable set
052     * @throws NullPointerException if set is null
053     * @since 4.0
054     */
055    public static <E> Set<E> unmodifiableSet(final Set<? extends E> set) {
056        if (set instanceof Unmodifiable) {
057            @SuppressWarnings("unchecked") // safe to upcast
058            final Set<E> tmpSet = (Set<E>) set;
059            return tmpSet;
060        }
061        return new UnmodifiableSet<>(set);
062    }
063
064    /**
065     * Constructor that wraps (not copies).
066     *
067     * @param set  the set to decorate, must not be null
068     * @throws NullPointerException if set is null
069     */
070    @SuppressWarnings("unchecked") // safe to upcast
071    private UnmodifiableSet(final Set<? extends E> set) {
072        super((Set<E>) set);
073    }
074
075    @Override
076    public boolean add(final E object) {
077        throw new UnsupportedOperationException();
078    }
079
080    @Override
081    public boolean addAll(final Collection<? extends E> coll) {
082        throw new UnsupportedOperationException();
083    }
084
085    @Override
086    public void clear() {
087        throw new UnsupportedOperationException();
088    }
089
090    @Override
091    public Iterator<E> iterator() {
092        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
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    /**
106     * @since 4.4
107     */
108    @Override
109    public boolean removeIf(final Predicate<? super E> filter) {
110        throw new UnsupportedOperationException();
111    }
112
113    @Override
114    public boolean retainAll(final Collection<?> coll) {
115        throw new UnsupportedOperationException();
116    }
117
118}