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

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 * 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.

 *

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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}/java.base/java/util/package-summary.html#CollectionsFramework">

 * Java Collections Framework</a>.

 *

 * @apiNote

 * An {@link Enumeration} can be converted into an {@code Iterator} by

 * using the {@link Enumeration#asIterator} method.

 *

 * @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}.

     * <p>

     * 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, unless an overriding class has specified a

     * concurrent modification policy.

     * <p>

     * The behavior of an iterator is unspecified if this method is called

     * after a call to the {@link #forEachRemaining forEachRemaining} 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 until all elements

     * have been processed or the action throws an exception.  Actions are

     * performed in the order of iteration, if that order is specified.

     * Exceptions thrown by the action are relayed to the caller.

     * <p>

     * The behavior of an iterator is unspecified if the action modifies the

     * collection in any way (even by calling the {@link #remove remove} method

     * or other mutator methods of {@code Iterator} subtypes),

     * unless an overriding class has specified a concurrent modification policy.

     * <p>

     * Subsequent behavior of an iterator is unspecified if the action throws an

     * exception.

     *

     * @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());

    }

}