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.ListIterator;
020
021import org.apache.commons.collections4.Unmodifiable;
022
023/**
024 * Decorates a list 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 UnmodifiableListIterator<E> implements ListIterator<E>, Unmodifiable {
032
033    /** The iterator being decorated */
034    private final ListIterator<? extends E> iterator;
035
036    //-----------------------------------------------------------------------
037    /**
038     * Decorates the specified iterator such that it cannot be modified.
039     *
040     * @param <E>  the element type
041     * @param iterator  the iterator to decorate
042     * @return a new unmodifiable list iterator
043     * @throws NullPointerException if the iterator is null
044     */
045    public static <E> ListIterator<E> umodifiableListIterator(final ListIterator<? extends E> iterator) {
046        if (iterator == null) {
047            throw new NullPointerException("ListIterator must not be null");
048        }
049        if (iterator instanceof Unmodifiable) {
050            @SuppressWarnings("unchecked") // safe to upcast
051            final ListIterator<E> tmpIterator = (ListIterator<E>) iterator;
052            return tmpIterator;
053        }
054        return new UnmodifiableListIterator<>(iterator);
055    }
056
057    //-----------------------------------------------------------------------
058    /**
059     * Constructor.
060     *
061     * @param iterator  the iterator to decorate
062     */
063    private UnmodifiableListIterator(final ListIterator<? extends E> iterator) {
064        super();
065        this.iterator = iterator;
066    }
067
068    //-----------------------------------------------------------------------
069    @Override
070    public boolean hasNext() {
071        return iterator.hasNext();
072    }
073
074    @Override
075    public E next() {
076        return iterator.next();
077    }
078
079    @Override
080    public int nextIndex() {
081        return iterator.nextIndex();
082    }
083
084    @Override
085    public boolean hasPrevious() {
086        return iterator.hasPrevious();
087    }
088
089    @Override
090    public E previous() {
091        return iterator.previous();
092    }
093
094    @Override
095    public int previousIndex() {
096        return iterator.previousIndex();
097    }
098
099    @Override
100    public void remove() {
101        throw new UnsupportedOperationException("remove() is not supported");
102    }
103
104    @Override
105    public void set(final E obj) {
106        throw new UnsupportedOperationException("set() is not supported");
107    }
108
109    @Override
110    public void add(final E obj) {
111        throw new UnsupportedOperationException("add() is not supported");
112    }
113
114}