This document discusses Java lists and iterators. It provides information on: 1) The List interface and classes that implement it like ArrayList and LinkedList. It also discusses how to create and output List objects. 2) Common List methods like isEmpty(), size(), add(), get(), and the iterator() method. 3) Using iterators to traverse List elements, including the iterator interface methods and how to use a generic iterator in a for-each loop. 4) Differences between using an iterator versus a for-each loop, where an iterator is needed to remove elements from the List.

1. List and Iterator

2. List Interface
• Java has 3 classes which implement the List
Interface - LinkedList, ArrayList and Vector.
• How do you use the ArrayList in your
program?
• import java.util.*
• How to create a List object?
• List lst = new ArrayList();
• Can we do this? Why?
• List lst = new List();

3. • How to output the List object?
• With the List object, we don’t need to use
loop structure to print out each element,
simply output the List object. Only the output
will be surrounded by square brackets.
• Name some of the List methods.
• boolean isEmpty()
• int size()
• Object set(int index, Object o)
• void add(int index, Object o)
• boolean add(Object o)
• Iterator<E> iterator()

4. • Do we need to cast the element retrieved
from a list object?
• Yes, unless the list object was created using
type parameters, meaning?
• List doubleList = new ArrayList();
• /* fill in the Arraylist with some Double objects */
• Double aDouble = doubleList.get(0); => ok?
• List<Double> doubleList = new ArrayList<Double>();

5. List Interface
• List interface. What is an interface? P135
1) All methods in the interface are both public
and abstract.
2) Any class implementing the interface has to
implement every method, otherwise…
• More rule on p139.

6. Iterator
• What is Iteration?
• Iteration is a continual repeating of
something.
• What java structure fits this description?
• Loops are iteration structure
• What is an iterator?
• An iterator’a sole purpose is to traverse a
collection, one element at a time.
• Is Iterator a class?
• NO, it is an interface.

7. • What are the 3 methods of the Iterator?
• boolean hasNext(); E next(); void remove()
• How to use a generic iterator?
• List<String> list = new ArrayList<String>();
<code to initialize list with strings>
Iterator<String> itr = list.iterator();
while(itr.hasNext())
System.out.println(itr.next())
• What is above while loop equivalent to?
• for-each loop

8. practice
• Write down the answers on the paper.
• Write a generic List object of Integer.
• Get an iterator from the List object.
• Loop through the list and if the number is not
mutiples of 3, remove it.

9. What is wrong with the codes?
Iterator<someType) itr = list.iterator();
while(true)
System.out.println(itr.next());
Iterator<someType) itr = list.iterator();
someType ob= itr.next();
itr.remove();
itr.remove();

10. • What is the different to use iterator from for-
each loop
• Use a for-each loop for accessing and
modifying objects in a list. Use an iterator for
removal of objects.

11. Homework
• Read Barron’s chapter 7 and BPJ lesson 40
about recursion. Write down any notes that
you think are important. They can be in any
form like questions and answers, or simply
questions which you don’t understand.
Everyone has to submit at least 25 notes or
remarks.