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 * Copyright (c) 1997, 2013, 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;

import java.util.function.Consumer;

/**

 * An iterator over a collection.  {@code Iterator} takes the place of

 * {@link Enumeration} in the Java Collections Framework.  Iterators

 * differ from enumerations in two ways:

 *

 * <ul>

 *      <li> Iterators allow the caller to remove elements from the

 *           underlying collection during the iteration with well-defined

 *           semantics.

 *      <li> Method names have been improved.

 * </ul>

 *

 * <p>This interface is a member of the

 * <a href="{@docRoot}/../technotes/guides/collections/index.html">

 * Java Collections Framework</a>.

 *

 * @param <E> the type of elements returned by this iterator

 *

 * @author  Josh Bloch

 * @see Collection

 * @see ListIterator

 * @see Iterable

 * @since 1.2

 */

public interface Iterator<E> {

    /**

     * Returns {@code true} if the iteration has more elements.

     * (In other words, returns {@code true} if {@link #next} would

     * return an element rather than throwing an exception.)

     *

     * @return {@code true} if the iteration has more elements

     */

    boolean hasNext();

    /**

     * Returns the next element in the iteration.

     *

     * @return the next element in the iteration

     * @throws NoSuchElementException if the iteration has no more elements

     */

    E next();

    /**

     * Removes from the underlying collection the last element returned

     * by this iterator (optional operation).  This method can be called

     * only once per call to {@link #next}.  The behavior of an iterator

     * is unspecified if the underlying collection is modified while the

     * iteration is in progress in any way other than by calling this

     * method.

     *

     * @implSpec

     * The default implementation throws an instance of

     * {@link UnsupportedOperationException} and performs no other action.

     *

     * @throws UnsupportedOperationException if the {@code remove}

     *         operation is not supported by this iterator

     *

     * @throws IllegalStateException if the {@code next} method has not

     *         yet been called, or the {@code remove} method has already

     *         been called after the last call to the {@code next}

     *         method

     */

    default void remove() {

        throw new UnsupportedOperationException("remove");

    }

    /**

     * Performs the given action for each remaining element, in the order

     * elements occur when iterating, until all elements have been processed or

     * the action throws an exception.  Errors or runtime exceptions thrown by

     * the action are relayed to the caller.

     *

     * @implSpec

     * <p>The default implementation behaves as if:

     * <pre>{@code

     *     while (hasNext())

     *         action.accept(next());

     * }</pre>

     *

     * @param action The action to be performed for each element

     * @throws NullPointerException if the specified action is null

     * @since 1.8

     */

    default void forEachRemaining(Consumer<? super E> action) {

        Objects.requireNonNull(action);

        while (hasNext())

            action.accept(next());

    }

}