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.Collection;
020import java.util.Enumeration;
021import java.util.Iterator;
022
023/**
024 * Adapter to make {@link Enumeration Enumeration} instances appear
025 * to be {@link Iterator Iterator} instances.
026 *
027 * @param <E> the type of elements returned by this iterator.
028 * @since 1.0
029 */
030public class EnumerationIterator<E> implements Iterator<E> {
031
032    /** The collection to remove elements from */
033    private final Collection<? super E> collection;
034    /** The enumeration being converted */
035    private Enumeration<? extends E> enumeration;
036    /** The last object retrieved */
037    private E last;
038
039    // Constructors
040    /**
041     * Constructs a new {@code EnumerationIterator} that will not
042     * function until {@link #setEnumeration(Enumeration)} is called.
043     */
044    public EnumerationIterator() {
045        this(null, null);
046    }
047
048    /**
049     * Constructs a new {@code EnumerationIterator} that provides
050     * an iterator view of the given enumeration.
051     *
052     * @param enumeration  the enumeration to use
053     */
054    public EnumerationIterator(final Enumeration<? extends E> enumeration) {
055        this(enumeration, null);
056    }
057
058    /**
059     * Constructs a new {@code EnumerationIterator} that will remove
060     * elements from the specified collection.
061     *
062     * @param enumeration  the enumeration to use
063     * @param collection  the collection to remove elements from
064     */
065    public EnumerationIterator(final Enumeration<? extends E> enumeration, final Collection<? super E> collection) {
066        this.enumeration = enumeration;
067        this.collection = collection;
068        this.last = null;
069    }
070
071    // Properties
072    /**
073     * Returns the underlying enumeration.
074     *
075     * @return the underlying enumeration
076     */
077    public Enumeration<? extends E> getEnumeration() {
078        return enumeration;
079    }
080
081    // Iterator interface
082    /**
083     * Returns true if the underlying enumeration has more elements.
084     *
085     * @return true if the underlying enumeration has more elements
086     * @throws NullPointerException  if the underlying enumeration is null
087     */
088    @Override
089    public boolean hasNext() {
090        return enumeration.hasMoreElements();
091    }
092
093    /**
094     * Returns the next object from the enumeration.
095     *
096     * @return the next object from the enumeration
097     * @throws NullPointerException if the enumeration is null
098     */
099    @Override
100    public E next() {
101        last = enumeration.nextElement();
102        return last;
103    }
104
105    /**
106     * Removes the last retrieved element if a collection is attached.
107     * <p>
108     * Functions if an associated {@code Collection} is known.
109     * If so, the first occurrence of the last returned object from this
110     * iterator will be removed from the collection.
111     *
112     * @throws IllegalStateException {@code next()} not called.
113     * @throws UnsupportedOperationException if no associated collection
114     */
115    @Override
116    public void remove() {
117        if (collection == null) {
118            throw new UnsupportedOperationException("No Collection associated with this Iterator");
119        }
120        if (last == null) {
121            throw new IllegalStateException("next() must have been called for remove() to function");
122        }
123        collection.remove(last);
124    }
125
126    /**
127     * Sets the underlying enumeration.
128     *
129     * @param enumeration  the new underlying enumeration
130     */
131    public void setEnumeration(final Enumeration<? extends E> enumeration) {
132        this.enumeration = enumeration;
133    }
134
135}