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 *      https://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 */
017
018package org.apache.commons.collections4;
019
020import java.util.ArrayList;
021import java.util.Enumeration;
022import java.util.List;
023import java.util.Set;
024import java.util.StringTokenizer;
025
026import org.apache.commons.collections4.iterators.EnumerationIterator;
027import org.apache.commons.collections4.iterators.IteratorIterable;
028
029/**
030 * Provides utility methods for {@link Enumeration} instances.
031 *
032 * @since 3.0
033 */
034public class EnumerationUtils {
035
036    /**
037     * Creates an {@link Iterable} that wraps an {@link Enumeration}. The returned {@link Iterable} can be used for a single iteration.
038     *
039     * @param <T>         The element type.
040     * @param enumeration The enumeration to use, may not be null.
041     * @return A new, single use {@link Iterable}.
042     * @throws NullPointerException if enumeration is null.
043     * @since 4.5.0-M1
044     */
045    public static <T> Iterable<T> asIterable(final Enumeration<T> enumeration) {
046        return new IteratorIterable<>(new EnumerationIterator<>(enumeration));
047    }
048
049    /**
050     * Gets the {@code index}-th value in the {@link Enumeration}, throwing {@code IndexOutOfBoundsException} if there is no such element.
051     * <p>
052     * The Enumeration is advanced to {@code index} (or to the end, if {@code index} exceeds the number of entries) as a side effect of this method.
053     * </p>
054     *
055     * @param enumeration     The enumeration to get a value from.
056     * @param index The index to get.
057     * @param <T>   The type of object in the {@link Enumeration}.
058     * @return The object at the specified index.
059     * @throws IndexOutOfBoundsException if the index is invalid.
060     * @throws IllegalArgumentException  if the object type is invalid.
061     * @throws NullPointerException      if enumeration is null.
062     * @since 4.1
063     */
064    public static <T> T get(final Enumeration<T> enumeration, final int index) {
065        CollectionUtils.checkIndexBounds(index);
066        int i = index;
067        while (enumeration.hasMoreElements()) {
068            i--;
069            if (i == -1) {
070                return enumeration.nextElement();
071            }
072            enumeration.nextElement();
073        }
074        throw new IndexOutOfBoundsException("Entry does not exist: " + i);
075    }
076
077    /**
078     * Creates a list based on an enumeration.
079     * <p>
080     * As the enumeration is traversed, an ArrayList of its values is created. The new list is returned.
081     * </p>
082     *
083     * @param <E>         The element type.
084     * @param enumeration The enumeration to traverse, which should not be {@code null}.
085     * @return A list containing all elements of the given enumeration.
086     * @throws NullPointerException if the enumeration parameter is {@code null}.
087     */
088    public static <E> List<E> toList(final Enumeration<? extends E> enumeration) {
089        return IteratorUtils.toList(new EnumerationIterator<>(enumeration));
090    }
091
092    /**
093     * Override toList(Enumeration) for StringTokenizer as it implements Enumeration&lt;Object&gt; for the sake of backward compatibility.
094     *
095     * @param stringTokenizer The tokenizer to convert to a {@link List}&lt;{@link String}&gt;
096     * @return A list containing all tokens of the given StringTokenizer.
097     */
098    public static List<String> toList(final StringTokenizer stringTokenizer) {
099        final List<String> result = new ArrayList<>(stringTokenizer.countTokens());
100        while (stringTokenizer.hasMoreTokens()) {
101            result.add(stringTokenizer.nextToken());
102        }
103        return result;
104    }
105
106    /**
107     * Creates a set based on an enumeration.
108     * <p>
109     * As the enumeration is traversed, an HashSet of its values is created. The new set is returned.
110     * </p>
111     *
112     * @param <E>         The element type.
113     * @param enumeration The enumeration to traverse, which should not be {@code null}.
114     * @return A set containing all elements of the given enumeration.
115     * @throws NullPointerException if the enumeration parameter is {@code null}.
116     * @since 4.5.0-M4
117     */
118    public static <E> Set<E> toSet(final Enumeration<? extends E> enumeration) {
119        return IteratorUtils.toSet(new EnumerationIterator<>(enumeration));
120    }
121
122    /**
123     * Don't allow instances.
124     */
125    private EnumerationUtils() {
126        // no instances.
127    }
128}