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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.StringTokenizer;

import org.apache.commons.collections4.iterators.EnumerationIterator;
import org.apache.commons.collections4.iterators.IteratorIterable;

/**
 * Provides utility methods for {@link Enumeration} instances.
 *
 * @since 3.0
 */
public class EnumerationUtils {

    /**
     * Creates an {@link Iterable} that wraps an {@link Enumeration}. The returned {@link Iterable} can be used for a
     * single iteration.
     *
     * @param  the element type
     * @param enumeration the enumeration to use, may not be null
     * @return a new, single use {@link Iterable}
     * @since 4.5.0-M1
     */
    public static  Iterable asIterable(final Enumeration enumeration) {
        return new IteratorIterable<>(new EnumerationIterator<>(enumeration));
    }

    /**
     * Returns the {@code index}-th value in the {@link Enumeration}, throwing
     * {@code IndexOutOfBoundsException} if there is no such element.
     * 
     * 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.
     * 
     *
     * @param e  the enumeration to get a value from
     * @param index  the index to get
     * @param  the type of object in the {@link Enumeration}
     * @return the object at the specified index
     * @throws IndexOutOfBoundsException if the index is invalid
     * @throws IllegalArgumentException if the object type is invalid
     * @since 4.1
     */
    public static  T get(final Enumeration e, final int index) {
        CollectionUtils.checkIndexBounds(index);
        int i = index;
        while (e.hasMoreElements()) {
            i--;
            if (i == -1) {
                return e.nextElement();
            }
            e.nextElement();
        }
        throw new IndexOutOfBoundsException("Entry does not exist: " + i);
    }

    /**
     * Creates a list based on an enumeration.
     *
     * As the enumeration is traversed, an ArrayList of its values is
     * created. The new list is returned.
     *
     * @param  the element type
     * @param enumeration  the enumeration to traverse, which should not be {@code null}.
     * @return a list containing all elements of the given enumeration
     * @throws NullPointerException if the enumeration parameter is {@code null}.
     */
    public static  List toList(final Enumeration enumeration) {
        return IteratorUtils.toList(new EnumerationIterator<>(enumeration));
    }

    /**
     * Override toList(Enumeration) for StringTokenizer as it implements Enumeration<Object>
     * for the sake of backward compatibility.
     *
     * @param stringTokenizer  the tokenizer to convert to a {@link List}<{@link String}>
     * @return a list containing all tokens of the given StringTokenizer
     */
    public static List toList(final StringTokenizer stringTokenizer) {
        final List result = new ArrayList<>(stringTokenizer.countTokens());
        while (stringTokenizer.hasMoreTokens()) {
            result.add(stringTokenizer.nextToken());
        }
        return result;
    }

    /**
     * Don't allow instances.
     */
    private EnumerationUtils() {
        // no instances.
    }

}