    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.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 * Attempts to modify it will result in an UnsupportedOperationException.
    028 * </p>
    029 *
    030 * @param <E> the type of elements returned by this iterator.
    031 * @since 3.0
    032 */
    033public final class UnmodifiableIterator<E> implements Iterator<E>, Unmodifiable {
    034
    035    /**
    036     * Decorates the specified iterator such that it cannot be modified.
    037     * <p>
    038     * If the iterator is already unmodifiable it is returned directly.
    039     *
    040     * @param <E>  the element type
    041     * @param iterator  the iterator to decorate
    042     * @return a new unmodifiable iterator
    043     * @throws NullPointerException if the iterator is null
    044     */
    045    public static <E> Iterator<E> unmodifiableIterator(final Iterator<? extends E> iterator) {
    046        Objects.requireNonNull(iterator, "iterator");
    047        if (iterator instanceof Unmodifiable) {
    048            @SuppressWarnings("unchecked") // safe to upcast
    049            final Iterator<E> tmpIterator = (Iterator<E>) iterator;
    050            return tmpIterator;
    051        }
    052        return new UnmodifiableIterator<>(iterator);
    053    }
    054
    055    /** The iterator being decorated */
    056    private final Iterator<? extends E> iterator;
    057
    058    /**
    059     * Constructs a new instance.
    060     *
    061     * @param iterator  the iterator to decorate
    062     */
    063    private UnmodifiableIterator(final Iterator<? extends E> iterator) {
    064        this.iterator = iterator;
    065    }
    066
    067    @Override
    068    public boolean hasNext() {
    069        return iterator.hasNext();
    070    }
    071
    072    @Override
    073    public E next() {
    074        return iterator.next();
    075    }
    076
    077    @Override
    078    public void remove() {
    079        throw new UnsupportedOperationException("remove() is not supported");
    080    }
    081
    082}