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?