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## java.util
Interface ListIterator

All Superinterfaces:
  Iterator

public interface ListIterator
extends Iterator

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 `remove()` and `set(Object)` methods are not defined in terms of the cursor position; they are defined to operate on the last element returned by a call to `next()` or `previous()`.

Since:
  1.2
See Also:
  `Collection`, `List`, `Iterator`, `Enumeration`

Method Summary
`void` | `add(Object 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.
`Object` | `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`.
`Object` | `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(Object o)` Replaces the last element returned by `next` or `previous` with the specified element (optional operation).

Method Detail

### hasNext

    public boolean 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.)

  Specified by:
    `hasNext` in interface `Iterator`
  Returns:
    `true` if the list iterator has more elements when traversing the list in the forward direction.

### next

    public Object next()

  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.)

  Specified by:
    `next` in interface `Iterator`
  Returns:
    the next element in the list.
  Throws:
    `NoSuchElementException` - if the iteration has no next element.

### hasPrevious

    public boolean 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.

### previous

    public Object previous()

  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.

### nextIndex

    public int 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.

### previousIndex

    public int 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

    public void 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`.

  Specified by:
    `remove` in interface `Iterator`
  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

    public void set(Object o)

  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`.

### add

    public void add(Object o)

  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.

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.