    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 *      https://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.iterators;
    018
    019import java.util.Iterator;
    020import java.util.Objects;
    021
    022import org.apache.commons.collections4.Unmodifiable;
    023
    024/**
    025 * Decorates an iterator such that it cannot be modified.
    026 * <p>
    027 * Calling {@link #remove()} throws {@link UnsupportedOperationException}.
    028 * </p>
    029 *
    030 * @param <E> The type of elements returned by this iterator.
    031 * @param <T> The wrapped Iterator type.
    032 * @since 3.0
    033 */
    034public final class UnmodifiableIterator<E, T extends Iterator<? extends E>> implements Iterator<E>, Unmodifiable {
    035
    036    /**
    037     * Decorates the specified iterator such that it cannot be modified.
    038     * <p>
    039     * If the iterator is already unmodifiable it is returned directly.
    040     * </p>
    041     *
    042     * @param <E>  the element type
    043     * @param iterator  The iterator to decorate
    044     * @return A new unmodifiable iterator
    045     * @throws NullPointerException if the iterator is null
    046     */
    047    public static <E> Iterator<E> unmodifiableIterator(final Iterator<? extends E> iterator) {
    048        Objects.requireNonNull(iterator, "iterator");
    049        if (iterator instanceof Unmodifiable) {
    050            @SuppressWarnings("unchecked") // safe to upcast
    051            final Iterator<E> tmpIterator = (Iterator<E>) iterator;
    052            return tmpIterator;
    053        }
    054        return wrap(iterator);
    055    }
    056
    057    static <E, T extends Iterator<? extends E>> UnmodifiableIterator<E, T> wrap(final T iterator) {
    058        return new UnmodifiableIterator<>(iterator);
    059    }
    060
    061    /**
    062     * The decorated iterator.
    063     */
    064    private final T iterator;
    065
    066    /**
    067     * Constructs a new instance.
    068     *
    069     * @param iterator  The iterator to decorate.
    070     */
    071    private UnmodifiableIterator(final T iterator) {
    072        this.iterator = iterator;
    073    }
    074
    075    @Override
    076    public boolean hasNext() {
    077        return iterator.hasNext();
    078    }
    079
    080    @Override
    081    public E next() {
    082        return iterator.next();
    083    }
    084
    085    /**
    086     * Always throws {@link UnsupportedOperationException}.
    087     *
    088     * @throws UnsupportedOperationException Always thrown.
    089     */
    090    // TODO This method can be removed in 5.0 since it's implemented as a default method in Iterator.
    091    @Override
    092    public void remove() {
    093        throw new UnsupportedOperationException("remove");
    094    }
    095
    096    T unwrap() {
    097        return iterator;
    098    }
    099}