1. COMP 121
Week 9: ArrayList

2. Objectives To understand the List interface
To examine how the List interface is implemented by the ArrayList class
To introduce the Iterator and Iterable interfaces
To review the enhanced for statement

3. List Interface
A list is an expandable collection of elements in which each element has a position or index
Some lists allow random access
Other lists allow sequential access
Allowed operations on the List interface include:
Finding a specified target
Adding an element to either end
Removing an item from either end
Traversing the list structure without a subscript
Not all classes perform the allowed operations with the same degree of efficiency
List classes provide the ability to store references to Objects
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

4. List Interface and ArrayList Class
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

5. ArrayList Class Simplest class that implements the List interface
Improvement over an array
Used when a programmer wants to add new elements to the end of a list but still needs the capability to access the elements stored in the list in arbitrary order
The size of an ArrayList automatically increases as new elements are added
The size method returns the current size
The capacity of an ArrayList is the number of elements an ArrayList can store (automatically increased)
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

6. ArrayList Class (cont’d)
The add method can:
Add an element at the end of the ArrayList
myList.add(“Bashful”);
myList.add(“Awful”);
myList.add(“Jumpy”);
myList.add(“Happy”);
Add an element at a certain subscript position
myList.add(2,”Doc”);
Subsequent calls to the add method will add at the end of the ArrayList
myList.add(“Dopey”);
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

7. ArrayList Class (cont’d)
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

8. ArrayList Class (cont’d)
The remove method can:
Remove an element at a certain subscript position
myList.remove(2);
You cannot access an ArrayList element directly using a subscript, but you can use the get/set methods
String dwarf = myList.get(2);
myList.set(2,”Sneezy”);
You can search an ArrayList for an element
Uses the equals method
myList.indexOf(“Sneezy”);
Will return a -1 if the element is not found
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

9. The ArrayList Class (cont’d)
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

10. Specification of the ArrayList Class
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

11. Iterator<E> Interface
The Iterator interface is defined as part of API package java.util
The List interface declares the method called iterator, which returns an Iterator object that will iterate over the elements of that list
An Iterator does not refer to or point to a particular node at any given time but points between nodes
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

12. The Iterator<E> Interface (cont’d)
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

13. Iterable Interface
This interface requires only that a class that implements it provide an iterator method
The Collection interface extends the Iterable interface, so all classes that implement the List interface (a subinterface of Collection) must provide an iterator method
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

14. The Enhanced for Statement
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

15. Enhanced for Statement
Is another way of doing …
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

16. Summary
The List interface defines an expandable collection of elements in which each element has a position or index
Elements in a List can be accessed using an index
The Java API provides the ArrayList<E> class, which uses an array as the underlying structure to implement the List
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

17. Summary (cont’d)
An iterator provides the ability to access the items in a List or Collection sequentially
The Iterator interface defines the methods available to an iterator
The Iterable interface is extended by the Collection interface at the root of the Collection hierarchy
The enhanced for statement makes it easy to iterate through a collection (or an array) without explicitly using an iterator
Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

18. Any Questions?