EnumerationUtils.java

/*
 * 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;

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

    /**
     * EnumerationUtils is not normally instantiated.
     */
    private EnumerationUtils() {}

    /**
     * Returns the <code>index</code>-th value in the {@link Enumeration}, throwing
     * <code>IndexOutOfBoundsException</code> if there is no such element.
     * <p>
     * The Enumeration is advanced to <code>index</code> (or to the end, if
     * <code>index</code> 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 <T> 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> T get(final Enumeration<T> e, final int index) {
        int i = index;
        CollectionUtils.checkIndexBounds(i);
        while (e.hasMoreElements()) {
            i--;
            if (i == -1) {
                return e.nextElement();
            } else {
                e.nextElement();
            }
        }
        throw new IndexOutOfBoundsException("Entry does not exist: " + i);
    }

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