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 Java Collections Framework
 *
 * @param <E> the type of the elements in the list
 *
 * @see Collection
 * @see List
 * @see Iterator
 * @see Enumeration
 * @see List#listIterator()
 */
public interface ListIterator<E> extends Iterator<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);

    /**
     * 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 {@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 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 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 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 #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();

    /**
     * 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);
}