/*

 * Copyright 1997-2007 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.util;

/**

 * An iterator for lists that allows the programmer

 * to traverse the list in either direction, modify

 * the list during iteration, and obtain the iterator's

 * current position in the list. A {@code ListIterator}

 * has no current element; its <I>cursor position</I> always

 * lies between the element that would be returned by a call

 * to {@code previous()} and the element that would be

 * returned by a call to {@code next()}.

 * An iterator for a list of length {@code n} has {@code n+1} possible

 * cursor positions, as illustrated by the carets ({@code ^}) below:

 * <PRE>

 *                      Element(0)   Element(1)   Element(2)   ... Element(n-1)

 * cursor positions:  ^            ^            ^            ^                  ^

 * </PRE>

 * Note that the {@link #remove} and {@link #set(Object)} methods are

 * <i>not</i> defined in terms of the cursor position;  they are defined to

 * operate on the last element returned by a call to {@link #next} or

 * {@link #previous()}.

 *

 * <p>This interface is a member of the

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

 * Java Collections Framework</a>.

 *

 * @author  Josh Bloch

 * @see Collection

 * @see List

 * @see Iterator

 * @see Enumeration

 * @see List#listIterator()

 * @since   1.2

 */

public interface ListIterator<E> extends Iterator<E> {

    // Query Operations

    /**

     * Returns {@code true} if this list iterator has more elements when

     * traversing the list in the forward direction. (In other words,

     * returns {@code true} if {@link #next} would return an element rather

     * than throwing an exception.)

     *

     * @return {@code true} if the list iterator has more elements when

     *         traversing the list in the forward direction

     */

    boolean hasNext();

    /**

     * Returns the next element in the list and advances the cursor position.

     * This method may be called repeatedly to iterate through the list,

     * or intermixed with calls to {@link #previous} to go back and forth.

     * (Note that alternating calls to {@code next} and {@code previous}

     * will return the same element repeatedly.)

     *

     * @return the next element in the list

     * @throws NoSuchElementException if the iteration has no next element

     */

    E next();

    /**

     * Returns {@code true} if this list iterator has more elements when

     * traversing the list in the reverse direction.  (In other words,

     * returns {@code true} if {@link #previous} would return an element

     * rather than throwing an exception.)

     *

     * @return {@code true} if the list iterator has more elements when

     *         traversing the list in the reverse direction

     */

    boolean hasPrevious();

    /**

     * Returns the previous element in the list and moves the cursor

     * position backwards.  This method may be called repeatedly to

     * iterate through the list backwards, or intermixed with calls to

     * {@link #next} to go back and forth.  (Note that alternating calls

     * to {@code next} and {@code previous} will return the same

     * element repeatedly.)

     *

     * @return the previous element in the list

     * @throws NoSuchElementException if the iteration has no previous

     *         element

     */

    E previous();

    /**

     * Returns the index of the element that would be returned by a

     * subsequent call to {@link #next}. (Returns list size if the list

     * iterator is at the end of the list.)

     *

     * @return the index of the element that would be returned by a

     *         subsequent call to {@code next}, or list size if the list

     *         iterator is at the end of the list

     */

    int nextIndex();

    /**

     * Returns the index of the element that would be returned by a

     * subsequent call to {@link #previous}. (Returns -1 if the list

     * iterator is at the beginning of the list.)

     *

     * @return the index of the element that would be returned by a

     *         subsequent call to {@code previous}, or -1 if the list

     *         iterator is at the beginning of the list

     */

    int previousIndex();

    // Modification Operations

    /**

     * Removes from the list the last element that was returned by {@link

     * #next} or {@link #previous} (optional operation).  This call can

     * only be made once per call to {@code next} or {@code previous}.

     * It can be made only if {@link #add} has not been

     * called after the last call to {@code next} or {@code previous}.

     *

     * @throws UnsupportedOperationException if the {@code remove}

     *         operation is not supported by this list iterator

     * @throws IllegalStateException if neither {@code next} nor

     *         {@code previous} have been called, or {@code remove} or

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

     *         {@code next} or {@code previous}

     */

    void remove();

    /**

     * Replaces the last element returned by {@link #next} or

     * {@link #previous} with the specified element (optional operation).

     * This call can be made only if neither {@link #remove} nor {@link

     * #add} have been called after the last call to {@code next} or

     * {@code previous}.

     *

     * @param e the element with which to replace the last element returned by

     *          {@code next} or {@code previous}

     * @throws UnsupportedOperationException if the {@code set} operation

     *         is not supported by this list iterator

     * @throws ClassCastException if the class of the specified element

     *         prevents it from being added to this list

     * @throws IllegalArgumentException if some aspect of the specified

     *         element prevents it from being added to this list

     * @throws IllegalStateException if neither {@code next} nor

     *         {@code previous} have been called, or {@code remove} or

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

     *         {@code next} or {@code previous}

     */

    void set(E e);

    /**

     * Inserts the specified element into the list (optional operation).

     * The element is inserted immediately before the next element that

     * would be returned by {@link #next}, if any, and after the next

     * element that would be returned by {@link #previous}, if any.  (If the

     * list contains no elements, the new element becomes the sole element

     * on the list.)  The new element is inserted before the implicit

     * cursor: a subsequent call to {@code next} would be unaffected, and a

     * subsequent call to {@code previous} would return the new element.

     * (This call increases by one the value that would be returned by a

     * call to {@code nextIndex} or {@code previousIndex}.)

     *

     * @param e the element to insert

     * @throws UnsupportedOperationException if the {@code add} method is

     *         not supported by this list iterator

     * @throws ClassCastException if the class of the specified element

     *         prevents it from being added to this list

     * @throws IllegalArgumentException if some aspect of this element

     *         prevents it from being added to this list

     */

    void add(E e);

}