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;
018
019import java.util.ArrayList;
020import java.util.Enumeration;
021import java.util.List;
022import java.util.StringTokenizer;
023
024import org.apache.commons.collections4.iterators.EnumerationIterator;
025import org.apache.commons.collections4.iterators.IteratorIterable;
026
027/**
028 * Provides utility methods for {@link Enumeration} instances.
029 *
030 * @since 3.0
031 */
032public class EnumerationUtils {
033
034    /**
035     * Creates an {@link Iterable} that wraps an {@link Enumeration}. The returned {@link Iterable} can be used for a
036     * single iteration.
037     *
038     * @param <T> the element type
039     * @param enumeration the enumeration to use, may not be null
040     * @return a new, single use {@link Iterable}
041     * @since 4.5
042     */
043    public static <T> Iterable<T> asIterable(final Enumeration<T> enumeration) {
044        return new IteratorIterable<>(new EnumerationIterator<>(enumeration));
045    }
046
047    /**
048     * Returns the {@code index}-th value in the {@link Enumeration}, throwing
049     * {@code IndexOutOfBoundsException} if there is no such element.
050     * <p>
051     * The Enumeration is advanced to {@code index} (or to the end, if
052     * {@code index} exceeds the number of entries) as a side effect of this method.
053     *
054     * @param e  the enumeration to get a value from
055     * @param index  the index to get
056     * @param <T> the type of object in the {@link Enumeration}
057     * @return the object at the specified index
058     * @throws IndexOutOfBoundsException if the index is invalid
059     * @throws IllegalArgumentException if the object type is invalid
060     * @since 4.1
061     */
062    public static <T> T get(final Enumeration<T> e, final int index) {
063        CollectionUtils.checkIndexBounds(index);
064        int i = index;
065        while (e.hasMoreElements()) {
066            i--;
067            if (i == -1) {
068                return e.nextElement();
069            }
070            e.nextElement();
071        }
072        throw new IndexOutOfBoundsException("Entry does not exist: " + i);
073    }
074
075    /**
076     * Creates a list based on an enumeration.
077     *
078     * <p>As the enumeration is traversed, an ArrayList of its values is
079     * created. The new list is returned.</p>
080     *
081     * @param <E> the element type
082     * @param enumeration  the enumeration to traverse, which should not be {@code null}.
083     * @return a list containing all elements of the given enumeration
084     * @throws NullPointerException if the enumeration parameter is {@code null}.
085     */
086    public static <E> List<E> toList(final Enumeration<? extends E> enumeration) {
087        return IteratorUtils.toList(new EnumerationIterator<>(enumeration));
088    }
089
090    /**
091     * Override toList(Enumeration) for StringTokenizer as it implements Enumeration&lt;Object&gt;
092     * for the sake of backward compatibility.
093     *
094     * @param stringTokenizer  the tokenizer to convert to a {@link List}&lt;{@link String}&gt;
095     * @return a list containing all tokens of the given StringTokenizer
096     */
097    public static List<String> toList(final StringTokenizer stringTokenizer) {
098        final List<String> result = new ArrayList<>(stringTokenizer.countTokens());
099        while (stringTokenizer.hasMoreTokens()) {
100            result.add(stringTokenizer.nextToken());
101        }
102        return result;
103    }
104
105    /**
106     * Don't allow instances.
107     */
108    private EnumerationUtils() {
109        // no instances.
110    }
111
112}