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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.
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 * 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</code> method return successive elements of the
 * series.
 * <p>
 * For example, to print all elements of a <tt>Vector&lt;E&gt;</tt> <i>v</i>:
 * <pre>
 *   for (Enumeration&lt;E&gt; 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</code>.
 * <p>
 * NOTE: The functionality of this interface is duplicated by the Iterator
 * interface.  In addition, Iterator adds an optional remove operation, and
 * has shorter method names.  New implementations should consider using
 * Iterator in preference to Enumeration.
 *
 * @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</code> if and only if this enumeration object
     *           contains at least one more element to provide;
     *          <code>false</code> 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} whose elements are the same as the
     * elements of this {@code Enumeration}. The results are undefined
     * if this method is called more than once, or if this Enumeration's
     * other methods are called after {@code asIterator} has been called.
     *
     * @apiNote
     * This method is intended to help adapt code that produces
     * {@code Enumeration} instances to code that consumes {@code Iterator}
     * or {@code Iterable} instances. For example, the
     * {@link java.security.PermissionCollection PermissionCollection.elements()}
     * method returns an {@code Enumeration<Permission>}. This can be adapted
     * for use in an enhanced-for loop as follows:
     *
     * <pre>{@code
     *     PermissionCollection pc = ... ;
     *     Iterable<Permission> permsIterable = () -> pc.elements().asIterator();
     *     for (Permission p : permsIterable) {
     *         doSomethingWithPermission(p);
     *     }
     * }</pre>
     *
     * A {@code Stream<Permission>} could be created from an
     * {@code Enumeration<Permission>} as follows:
     *
     * <pre>{@code
     *     Stream<Permission> permsStream = StreamSupport.stream(
     *         Spliterators.spliteratorUnknownSize(
     *             pc.elements().asIterator(),
     *             Spliterator.ORDERED | Spliterator.IMMUTABLE),
     *         false);
     * }</pre>
     *
     * @implSpec
     * The returned Iterator's {@link Iterator#hasNext hasNext} method calls and returns
     * the value from this Enumeration's {@code hasMoreElements} method; its
     * {@link Iterator#next next} method calls and returns the value from this Enumeration's
     * {@code nextElement} method; and its {@link Iterator#remove remove} method throws
     * {@code UnsupportedOperationException}.
     *
     * @return an Iterator derived from this Enumeration
     *
     * @since 1.9
     */
    default Iterator<E> asIterator() {
        return new Iterator<E>() {
            @Override public boolean hasNext() {
                return Enumeration.this.hasMoreElements();
            }
            @Override public E next() {
                return Enumeration.this.nextElement();
            }
        };
    }
}