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 * Copyright (c) 1994, 2015, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.util;

/**

 * An object that implements the Enumeration interface generates a

 * series of elements, one at a time. Successive calls to the

 * {@code nextElement} method return successive elements of the

 * series.

 * <p>

 * For example, to print all elements of a {@code Vector<E>} <i>v</i>:

 * <pre>

 *   for (Enumeration<E> e = v.elements(); e.hasMoreElements();)

 *       System.out.println(e.nextElement());</pre>

 * <p>

 * Methods are provided to enumerate through the elements of a

 * vector, the keys of a hashtable, and the values in a hashtable.

 * Enumerations are also used to specify the input streams to a

 * {@code SequenceInputStream}.

 *

 * @apiNote

 * The functionality of this interface is duplicated by the {@link Iterator}

 * interface.  In addition, {@code Iterator} adds an optional remove operation,

 * and has shorter method names.  New implementations should consider using

 * {@code Iterator} in preference to {@code Enumeration}. It is possible to

 * adapt an {@code Enumeration} to an {@code Iterator} by using the

 * {@link #asIterator} method.

 *

 * @see     java.util.Iterator

 * @see     java.io.SequenceInputStream

 * @see     java.util.Enumeration#nextElement()

 * @see     java.util.Hashtable

 * @see     java.util.Hashtable#elements()

 * @see     java.util.Hashtable#keys()

 * @see     java.util.Vector

 * @see     java.util.Vector#elements()

 *

 * @author  Lee Boynton

 * @since   1.0

 */

public interface Enumeration<E> {

    /**

     * Tests if this enumeration contains more elements.

     *

     * @return  {@code true} if and only if this enumeration object

     *           contains at least one more element to provide;

     *          {@code false} otherwise.

     */

    boolean hasMoreElements();

    /**

     * Returns the next element of this enumeration if this enumeration

     * object has at least one more element to provide.

     *

     * @return     the next element of this enumeration.

     * @exception  NoSuchElementException  if no more elements exist.

     */

    E nextElement();

    /**

     * Returns an {@link Iterator} that traverses the remaining elements

     * covered by this enumeration. Traversal is undefined if any methods

     * are called on this enumeration after the call to {@code asIterator}.

     *

     * @apiNote

     * This method is intended to help adapt code that produces

     * {@code Enumeration} instances to code that consumes {@code Iterator}

     * instances. For example, the {@link java.util.jar.JarFile#entries

     * JarFile.entries()} method returns an {@code Enumeration<JarEntry>}.

     * This can be turned into an {@code Iterator}, and then the

     * {@code forEachRemaining()} method can be used:

     *

     * <pre>{@code

     *     JarFile jarFile = ... ;

     *     jarFile.entries().asIterator().forEachRemaining(entry -> { ... });

     * }</pre>

     *

     * (Note that there is also a {@link java.util.jar.JarFile#stream

     * JarFile.stream()} method that returns a {@code Stream} of entries,

     * which may be more convenient in some cases.)

     *

     * @implSpec

     * The default implementation returns an {@code Iterator} whose

     * {@link Iterator#hasNext hasNext} method calls this Enumeration's

     * {@code hasMoreElements} method, whose {@link Iterator#next next}

     * method calls this Enumeration's {@code nextElement} method, and

     * whose {@link Iterator#remove remove} method throws

     * {@code UnsupportedOperationException}.

     *

     * @return an Iterator representing the remaining elements of this Enumeration

     *

     * @since 9

     */

    default Iterator<E> asIterator() {

        return new Iterator<>() {

            @Override public boolean hasNext() {

                return hasMoreElements();

            }

            @Override public E next() {

                return nextElement();

            }

        };

    }

}