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 4.5.0-M1
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     * </p>
054     *
055     * @param e  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     * @since 4.1
062     */
063    public static <T> T get(final Enumeration<T> e, final int index) {
064        CollectionUtils.checkIndexBounds(index);
065        int i = index;
066        while (e.hasMoreElements()) {
067            i--;
068            if (i == -1) {
069                return e.nextElement();
070            }
071            e.nextElement();
072        }
073        throw new IndexOutOfBoundsException("Entry does not exist: " + i);
074    }
075
076    /**
077     * Creates a list based on an enumeration.
078     *
079     * <p>As the enumeration is traversed, an ArrayList of its values is
080     * created. The new list is returned.</p>
081     *
082     * @param <E> the element type
083     * @param enumeration  the enumeration to traverse, which should not be {@code null}.
084     * @return a list containing all elements of the given enumeration
085     * @throws NullPointerException if the enumeration parameter is {@code null}.
086     */
087    public static <E> List<E> toList(final Enumeration<? extends E> enumeration) {
088        return IteratorUtils.toList(new EnumerationIterator<>(enumeration));
089    }
090
091    /**
092     * Override toList(Enumeration) for StringTokenizer as it implements Enumeration&lt;Object&gt;
093     * 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     * Don't allow instances.
108     */
109    private EnumerationUtils() {
110        // no instances.
111    }
112
113}