    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;
    020
    021import org.apache.commons.collections4.Unmodifiable;
    022
    023/**
    024 * Decorates an iterator such that it cannot be modified.
    025 * <p>
    026 * Attempts to modify it will result in an UnsupportedOperationException.
    027 *
    028 * @since 3.0
    029 */
    030public final class UnmodifiableIterator<E> implements Iterator<E>, Unmodifiable {
    031
    032    /** The iterator being decorated */
    033    private final Iterator<? extends E> iterator;
    034
    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     *
    041     * @param <E>  the element type
    042     * @param iterator  the iterator to decorate
    043     * @return a new unmodifiable iterator
    044     * @throws NullPointerException if the iterator is null
    045     */
    046    public static <E> Iterator<E> unmodifiableIterator(final Iterator<? extends E> iterator) {
    047        if (iterator == null) {
    048            throw new NullPointerException("Iterator must not be null");
    049        }
    050        if (iterator instanceof Unmodifiable) {
    051            @SuppressWarnings("unchecked") // safe to upcast
    052            final Iterator<E> tmpIterator = (Iterator<E>) iterator;
    053            return tmpIterator;
    054        }
    055        return new UnmodifiableIterator<>(iterator);
    056    }
    057
    058    //-----------------------------------------------------------------------
    059    /**
    060     * Constructor.
    061     *
    062     * @param iterator  the iterator to decorate
    063     */
    064    private UnmodifiableIterator(final Iterator<? extends E> iterator) {
    065        super();
    066        this.iterator = iterator;
    067    }
    068
    069    //-----------------------------------------------------------------------
    070    @Override
    071    public boolean hasNext() {
    072        return iterator.hasNext();
    073    }
    074
    075    @Override
    076    public E next() {
    077        return iterator.next();
    078    }
    079
    080    @Override
    081    public void remove() {
    082        throw new UnsupportedOperationException("remove() is not supported");
    083    }
    084
    085}