Transcript COMP 121 Week 9

COMP 121
Week 9: ArrayList
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
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List Interface
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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
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Allowed operations on the List interface include:
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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.
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.
ArrayList Class
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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
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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.
ArrayList Class (cont’d)
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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.
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.
ArrayList Class (cont’d)
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The remove method can:
 Remove an element at
myList.remove(2);
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a certain subscript position
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”);
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You can search an ArrayList for an element
 Uses the equals method
myList.indexOf(“Sneezy”);
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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.
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.
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.
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
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Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using
Java Version 5.0. New York: John Wiley & Sons.
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.
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
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Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using
Java Version 5.0. New York: John Wiley & Sons.
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.
Enhanced for Statement
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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.
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
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Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using
Java Version 5.0. New York: John Wiley & Sons.
Summary (cont’d)
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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.
Any Questions?