1. CSC 205 – Java Programming II
Lecture 29
March 25, 2002

2. Drawbacks of LinkedList
Unsatisfactory performance when accessing elements by index
add(4, new Character(‘u’));
first
last A c c o n t 1 2 3 4 5 u

3. Solution: ListIterator
Methods defined in ListIterator
public boolean hasNext()
public boolean hasPrevious()
public Object next()
public Object previous()
public void remove()
public void add(Object o)
public void set(Object o)
public int nextIndex()
public int previousIndex ()

4. Example LinkedList letters = new LinkedList();
ListIterator lItr = letters.listIterator();
lItr.add(new Character('f'));
lItr.add(new Character('t'));
lItr.previous();
lItr.add(new Character('e'));
lItr.add(new Character('r'));
lItr.next();
lItr.add(new Character('c'));
lItr = letters.listIterator();
lItr.add(new Character('p'));

5. A perfect Example f t e r f t e r f e r t p e r f e r t first
First two add
and two previous
first
Two more add
one next e r f t
Two more
Add, one
list-
Iterator
first e r f e r t
first p e r f e r t

6. Creating ListIterator
Creating ListIterator through listIterator methods only
listIterator()
listIterator(int index)

7. Using ListIterator Relative positions: one convenient view
Interleaf ListIterator positions with element positions
first
last A c c o n t 1 2 3 4 5
listIterator()
listIterator(a.size())
listIterator(0)

8. Using ListIterator Adding elements itr.add(new Character(‘u’)); u A c
first
last A c c o n t 1 2 3 4 5
Current position of
The listIterator

9. Using ListIterator After adding ‘u’ into the list, we have
itr.next()  ‘n’
Itr.previous()  ‘u’
One problem: this loop never stops
lItr = fruits.
listIterator(fruits.size());
while (lItr.hasPrevious()) {
System.out.println(lItr.previous());
lItr.add("Pears"); }

10. Using ListIterator This loop works fine fruits.add("Kumquats");
fruits.add("Bananas");
fruits.add("Kiwi");
fruits.add("Apples");
lItr = fruits.listIterator();
while (lItr.hasNext()) {
System.out.println(lItr.next());
lItr.add("Pears"); }

11. Using ListIterator Relative positions: the normal view A c c o n t
first
last A c c o n t 1 2 3 4 5
listIterator()
listIterator(0)
listIterator(a.size())

12. Using ListIterator
The next method advances to the next position, but returns the element that had been in the current position
Similar to the post-increment operator (i++)
The previous method first retreats to the position before the current position, and then returns the element at that retreated-to position
Similar to the pre-decrement operator (--i)