ListIterator<E>

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 ListIterator has no current element; its cursor position always lies between the element that would be returned by a call to previous() and the element that would be returned by a call to next(). In a list of length n, there are n+1 valid index values, from 0 to n, inclusive.


          Element(0)   Element(1)   Element(2)   ... Element(n)   
        ^            ^            ^            ^               ^
 Index: 0            1            2            3               n+1

Note that the ListIterator and set methods are not defined in terms of the cursor position; they are defined to operate on the last element returned by a call to ListIterator or previous.

This interface is a member of the Java Collections Framework.

Since: 1.2

Version: 1.22, 02/17/03

Author: Josh Bloch

See Also: Collection List Iterator Enumeration "string" home

Method Summary
void	add(E o) Inserts the specified element into the list (optional operation).
boolean	hasNext() Returns `true` if this list iterator has more elements when traversing the list in the forward direction.
boolean	hasPrevious() Returns `true` if this list iterator has more elements when traversing the list in the reverse direction.
E	next() Returns the next element in the list.
int	nextIndex() Returns the index of the element that would be returned by a subsequent call to `next`.
E	previous() Returns the previous element in the list.
int	previousIndex() Returns the index of the element that would be returned by a subsequent call to `previous`.
void	remove() Removes from the list the last element that was returned by `next` or `previous` (optional operation).
void	set(E o) Replaces the last element returned by `next` or `previous` with the specified element (optional operation).

Method Detail

add

Inserts the specified element into the list (optional operation). The element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by 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 next would be unaffected, and a subsequent call to previous would return the new element. (This call increases by one the value that would be returned by a call to nextIndex or previousIndex.)

Parameters: o the element to insert.

Throws: UnsupportedOperationException if the add method is not supported by this list iterator. ClassCastException if the class of the specified element prevents it from being added to this list. IllegalArgumentException if some aspect of this element prevents it from being added to this list.

hasNext

Returns true if this list iterator has more elements when traversing the list in the forward direction. (In other words, returns true if next would return an element rather than throwing an exception.)

Returns: true if the list iterator has more elements when traversing the list in the forward direction.

hasPrevious

Returns true if this list iterator has more elements when traversing the list in the reverse direction. (In other words, returns true if previous would return an element rather than throwing an exception.)

Returns: true if the list iterator has more elements when traversing the list in the reverse direction.

Returns the next element in the list. This method may be called repeatedly to iterate through the list, or intermixed with calls to previous to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)

Returns: the next element in the list.

Throws: NoSuchElementException if the iteration has no next element.

nextIndex

Returns the index of the element that would be returned by a subsequent call to next. (Returns list size if the list iterator is at the end of the list.)

Returns: the index of the element that would be returned by a subsequent call to next, or list size if list iterator is at end of list.

Returns the previous element in the list. This method may be called repeatedly to iterate through the list backwards, or intermixed with calls to next to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)

Returns: the previous element in the list.

Throws: NoSuchElementException if the iteration has no previous element.

previousIndex

Returns the index of the element that would be returned by a subsequent call to previous. (Returns -1 if the list iterator is at the beginning of the list.)

Returns: the index of the element that would be returned by a subsequent call to previous, or -1 if list iterator is at beginning of list.

remove

Removes from the list the last element that was returned by next or previous (optional operation). This call can only be made once per call to next or previous. It can be made only if ListIterator.add has not been called after the last call to next or previous.

Throws: UnsupportedOperationException if the remove operation is not supported by this list iterator. IllegalStateException neither next nor previous have been called, or remove or add have been called after the last call to * next or previous.

set

Replaces the last element returned by next or previous with the specified element (optional operation). This call can be made only if neither ListIterator.remove nor ListIterator.add have been called after the last call to next or previous.

Parameters: o the element with which to replace the last element returned by next or previous.

Throws: UnsupportedOperationException if the set operation is not supported by this list iterator. ClassCastException if the class of the specified element prevents it from being added to this list. IllegalArgumentException if some aspect of the specified element prevents it from being added to this list. IllegalStateException if neither next nor previous have been called, or remove or add have been called after the last call to next or previous.

Interface ListIterator<E>