    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 * @since 1.0
    028 */
    029public class EnumerationIterator<E> implements Iterator<E> {
    030
    031    /** The collection to remove elements from */
    032    private final Collection<? super E> collection;
    033    /** The enumeration being converted */
    034    private Enumeration<? extends E> enumeration;
    035    /** The last object retrieved */
    036    private E last;
    037
    038    // Constructors
    039    //-----------------------------------------------------------------------
    040    /**
    041     * Constructs a new <code>EnumerationIterator</code> 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</code> 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</code> 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        super();
    067        this.enumeration = enumeration;
    068        this.collection = collection;
    069        this.last = null;
    070    }
    071
    072    // Iterator interface
    073    //-----------------------------------------------------------------------
    074    /**
    075     * Returns true if the underlying enumeration has more elements.
    076     *
    077     * @return true if the underlying enumeration has more elements
    078     * @throws NullPointerException  if the underlying enumeration is null
    079     */
    080    @Override
    081    public boolean hasNext() {
    082        return enumeration.hasMoreElements();
    083    }
    084
    085    /**
    086     * Returns the next object from the enumeration.
    087     *
    088     * @return the next object from the enumeration
    089     * @throws NullPointerException if the enumeration is null
    090     */
    091    @Override
    092    public E next() {
    093        last = enumeration.nextElement();
    094        return last;
    095    }
    096
    097    /**
    098     * Removes the last retrieved element if a collection is attached.
    099     * <p>
    100     * Functions if an associated <code>Collection</code> is known.
    101     * If so, the first occurrence of the last returned object from this
    102     * iterator will be removed from the collection.
    103     *
    104     * @throws IllegalStateException <code>next()</code> not called.
    105     * @throws UnsupportedOperationException if no associated collection
    106     */
    107    @Override
    108    public void remove() {
    109        if (collection != null) {
    110            if (last != null) {
    111                collection.remove(last);
    112            } else {
    113                throw new IllegalStateException("next() must have been called for remove() to function");
    114            }
    115        } else {
    116            throw new UnsupportedOperationException("No Collection associated with this Iterator");
    117        }
    118    }
    119
    120    // Properties
    121    //-----------------------------------------------------------------------
    122    /**
    123     * Returns the underlying enumeration.
    124     *
    125     * @return the underlying enumeration
    126     */
    127    public Enumeration<? extends E> getEnumeration() {
    128        return enumeration;
    129    }
    130
    131    /**
    132     * Sets the underlying enumeration.
    133     *
    134     * @param enumeration  the new underlying enumeration
    135     */
    136    public void setEnumeration(final Enumeration<? extends E> enumeration) {
    137        this.enumeration = enumeration;
    138    }
    139
    140}