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