    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 * </p>
    028 *
    029 * @since 3.0
    030 */
    031public final class UnmodifiableIterator<E> implements Iterator<E>, Unmodifiable {
    032
    033    /** The iterator being decorated */
    034    private final Iterator<? extends E> iterator;
    035
    036    //-----------------------------------------------------------------------
    037    /**
    038     * Decorates the specified iterator such that it cannot be modified.
    039     * <p>
    040     * If the iterator is already unmodifiable it is returned directly.
    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        if (iterator == null) {
    049            throw new NullPointerException("Iterator must not be null");
    050        }
    051        if (iterator instanceof Unmodifiable) {
    052            @SuppressWarnings("unchecked") // safe to upcast
    053            final Iterator<E> tmpIterator = (Iterator<E>) iterator;
    054            return tmpIterator;
    055        }
    056        return new UnmodifiableIterator<>(iterator);
    057    }
    058
    059    //-----------------------------------------------------------------------
    060    /**
    061     * Constructor.
    062     *
    063     * @param iterator  the iterator to decorate
    064     */
    065    private UnmodifiableIterator(final Iterator<? extends E> iterator) {
    066        super();
    067        this.iterator = iterator;
    068    }
    069
    070    //-----------------------------------------------------------------------
    071    @Override
    072    public boolean hasNext() {
    073        return iterator.hasNext();
    074    }
    075
    076    @Override
    077    public E next() {
    078        return iterator.next();
    079    }
    080
    081    @Override
    082    public void remove() {
    083        throw new UnsupportedOperationException("remove() is not supported");
    084    }
    085
    086}