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  *

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 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 element that

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

 }