ap.java.util
Interface ListIterator

All Superinterfaces:

Iterator

public interface ListIterator

extends Iterator

For the purposes of the AP subset (AB only) this interface is an Iterator with two additional methods for changing the collection of elements being iterated over.

Conceptually a ListIterator traverses a list as though there is a header node. Thus calling next is not valid for a ListIterator constructed from an empty list which conceptually has a header node but no node after the header node. However, calling add is valid for a ListIterator constructed from an empty list and will result in adding a new node after the header node, though this new value will not affect calls to next or to hasNext for the ListIterator.

The code below shows how to change the list

      ("hello", "goodbye")
 

to the list

      ("hello", "hello 2", "goodbye", "goodbye 2")
 

using a ListIterator.

  // double-up a list of strings
  public static void doubleUp(List list)
  {
      ListIterator it = list.listIterator();
      while (it.hasNext()) {
          String s = (String) it.next();
          it.add(s + " 2");
      }
  }
 

The code below changes the initially empty list being iterated over to a list with the string "first", but does not print anything.

        ArrayList list = new ArrayList();
        ListIterator it = list.listIterator();
        it.add("first");                         // add a first element
        while (it.hasNext()) {                   // but nothint printed
            System.out.println(it.next());       // by this loop
        } 
 

The code below uses set to "double" every string in a list, e.g., to change the list ("one", "two") to ("oneone", "twotwo").

       it = list.listIterator();
       while (it.hasNext()) {
           String s = (String) it.next();
           it.set(s+s);
       }
 

Method Summary

void	add(java.lang.Object o) Inserts the argument into the list being iterated over.
void	set(java.lang.Object o) Replaces the last element returned by next by the argument.

Methods inherited from interface ap.java.util.Iterator

hasNext, next, remove

Method Detail

add

public void add(java.lang.Object o)

Inserts the argument into the list being iterated over. The element is inserted before the element that would be returned by calling next if there is any such element, however the value returned by a subsequent call of next is not affected.

Parameters:

o - is the Object inserted into the collection being iterated over

Throws:

java.lang.UnsupportedOperationException - if add is not supported by this list iterator

set

public void set(java.lang.Object o)

Replaces the last element returned by next by the argument. It is not valid to call set if either add or remove have been called after the last call to next.

Parameters:

o - is the object that replaces the last element returned by next

Throws:

IllegalStateException - if next has not been called or if remove or add have been called after the last call of next

java.lang.UnsupportedOperationException - if set is not supported by this list iterator