CSC584 Enterprise
Programming
Chapter 1 – Review of object-oriented programming
MARSHIMA MOHD ROSLI
COMPUTER SCIENCE
Review of Object Oriented Programming
Concepts
Chapter 1
Outline a) Object Oriented Programming Concepts
◦ Objects, classes, packages
Forget programming for a while.
Think about the World and the things that
are in it.
◦ What things are objects? What things are not objects?
List four objects and list four non-objects in
the classroom.
Answer..
An object is made of tangible material (the pen is made of plastic,
metal, ink).
An object holds together as a single whole (the whole pen, not a fog).
An object has properties (the color of the pen, where it is, how thick it
writes...).
An object can do things and can have things done to it.
Characteristics of Objects
The last three items on the list seem clear enough. In fact,
they have names:
◦ An object has identity (it acts as a single whole).
◦ An object has state (it has various properties, which
might change).
◦ An object has behavior (it can do things and can have
things done to it).
More about objects..
Consider a tube of four yellow tennis
balls.
◦ Is the tube of tennis balls an object?
◦ Is each tennis ball an object?
◦ Could the top two balls be considered a single object?
◦ Is the color of the balls an object?
More about objects..
Is the tube of tennis balls an object?
◦ Yes. It has identity (my tube of balls is different than yours), it has state
(opened, unopened, brand name, location), and behavior (although not
much).
Is each tennis ball an object?
◦ Yes. It is OK for objects to be part of other objects. Although each ball has
nearly the same state and behavior as the others, each has its own identity.
Could the top two balls be considered a single object?
◦ Not ordinarily. Each has its own identity independent of the other. If they
were joined together with a stick you might consider them as one object.
Is the color of the balls an object?
◦ No. It is a property of each ball.
Software Objects as Memory
Objects (real world and software) have identity, state, and
behavior.
◦ Software objects have identity. Each is a distinct chunk of
memory. (Just like a yellow tennis ball, each software
object is a distinct individual even though it may look
nearly the same as other objects.)
Software Objects as Memory
Objects (real world and software) have identity, state, and
behavior.
◦ Software objects have state. Some of the memory that
makes up a software object is used for variables which
contain values. These values are the state of the object.
◦ Software objects have behavior. Some of the memory
that makes up a software object contains programs
(called methods) that enable the object to "do things".
The object does something when one of its method runs.
What Is an Object?
Informally, an object represents an entity, either physical,
conceptual, or software.
◦ Physical entity Truck
◦ Conceptual entity Chemical Process
◦ Software entity
Linked List
A More Formal Definition Attributes
An object is an entity with a well-
defined boundary and identity that
encapsulates state and behavior.
◦ State is represented by attributes
and relationships.
◦ Behavior is represented by
operations, methods, and state
machines.
Object
Operations
An Object Has State
State is a condition or situation during the life of an object, which satisfies some
condition, performs some activity, or waits for some event.
The state of an object normally changes over time.
Name: J Clark
Employee ID:
567138
HireDate:
07/25/1991
Status: Tenured
Name: J Clark Discipline:
Employee ID: 567138 Finance
Date Hired: July 25, 1991 MaxLoad: 3
Status: Tenured
Discipline: Finance Professor Clark
Maximum Course Load: 3 classes
An Object Has Behavior
Behavior determines how an object acts and reacts.
The visible behavior of an object is modeled by a set of messages it can respond
to (operations that the object can perform).
Professor Clark’s behavior
Submit Final Grades TakeSabbatical()
Accept Course Offering
Take Sabbatical
Professor Clark
Set Max Load
An Object Has Identity
Each object has a unique identity, even if the state is identical to that of another
object.
Professor “J Clark” Professor “J Clark”
teaches Biology teaches Biology
Basic Concept of Classes
First Example: Using the Bicycle Class
class BicycleRegistration {
public static void main(String[] args) {
Bicycle bike1, bike2;
String owner1, owner2;
bike1 = new Bicycle( ); //Create and assign values to bike1
bike1.setOwnerName("Adam Smith");
bike2 = new Bicycle( ); //Create and assign values to bike2
bike2.setOwnerName("Ben Jones");
owner1 = bike1.getOwnerName( ); //Output the information
owner2 = bike2.getOwnerName( );
System.out.println(owner1 + " owns a bicycle.");
System.out.println(owner2 + " also owns a bicycle.");
}
}
The Definition of the Bicycle Class
class Bicycle {
// Data Member
private String ownerName;
//Constructor: Initialzes the data member
public void Bicycle( ) {
ownerName = "Unknown";
}
//Returns the name of this bicycle's owner
public String getOwnerName( ) {
return ownerName;
}
//Assigns the name of this bicycle's owner
public void setOwnerName(String name) {
ownerName = name;
}
}
Multiple Instances
Once the Bicycle class is defined, we can create multiple instances.
bike1 bike2
Bicycle bike1, bike2;
: Bicycle : Bicycle
bike1 = new Bicycle( );
bike1.setOwnerName("Adam Smith");
ownerName ownerName
bike2 = new Bicycle( ); “Adam Smith” “Ben Jones”
bike2.setOwnerName("Ben Jones");
Sample Code
The Program Structure and
Source Files
BicycleRegistration Bicycle
There are two source files.
Each class definition is
stored in a separate file.
BicycleRegistration.java Bicycle.java
To run the program: 1. javac Bicycle.java (compile)
2. javac BicycleRegistration.java (compile)
3. java BicycleRegistration (run)
Template for Class Definition
Import Statements
Class Comment
class { Class Name
Data Members
Methods
(incl. Constructor)
}
Data Member Declaration
<modifiers> <data type> <name> ;
Modifiers Data Type Name
private String ownerName ;
Note: There’s only one modifier in this example.
Method Declaration
<modifier> <return type> <method name> ( <parameters> ){
<statements>
}
Modifier Return Type Method Name Parameter
public void setOwnerName ( String name ) {
ownerName = name; Statements
}
Quick Check!
1. Extend the Bicycle class by adding the second data
member tagNo of String. Declare this data member as
private.
2. Add new method to the Bicycle class that assigns a tag
number. This method will be called as follows:
Bicycle bike;
bike = new Bicycle( );
...
bike.setTagNo("2004-134R");
Constructor
A constructor is a special method that is executed when a new instance of the
class is created.
public <class name> ( <parameters> ){
<statements>
}
Modifier Class Name Parameter
public Bicycle ( ) {
ownerName = "Unassigned";
} Statements
Constructors
Type of constructor
◦ Default constructor (no argument)
public Bicycle() {
gear = 1; public Bicycle() {
cadence = 10;
speed = 0; }
}
◦ Normal constructor (with argument)
public Bicycle(int startCadence, int startSpeed, int startGear)
{
gear = startGear;
cadence = startCadence;
speed = startSpeed;
}
Constructors: Create new object
Default constructor (no argument)
public Bicycle() {
gear = 1;
cadence = 10;
speed = 0;
}
Constructor
Bicycle yourBike = new Bicycle();
Create a new Bicycle
object called yourBike
Constructors: Create new object
Normal constructor (with argument)
public Bicycle(int startCadence, int startSpeed, int startGear)
{
gear = startGear;
Constructor
cadence = startCadence;
speed = startSpeed;
}
Bicycle myBike = new Bicycle(30, 0, 8);
Create a new Bicycle
object called myBike
Quick Check!
1. Which of the following constructors are invalid?
public int ClassA(int one) { ……..}
public ClassB(int one, int two) {……..}
void ClassC( ) {…….}
2. Complete the following constructor :
class Test {
private double score;
public Test(double val) {
//assign the value of parameter to
//the data member
}
}
Accessor (get method)
//Returns String
public the name getOwnerName()
of this bicycle's owner
{
return ownerName;
}
• Return information about an object
• getOwnerName()– return information about who is the owner of a
bicycle
Mutator (set method)
//Assigns the name of this bicycle's owner
public void setOwnerName(String name)
{
ownerName = name;
}
• Mutator ‐ Sets a property(data,attrbute) of an object
• setOwnerName() is a mutator method
Second Example: Using Bicycle and Account
class SecondMain {
//This sample program uses both the Bicycle and Account classes
public static void main(String[] args) {
Bicycle bike;
Account acct;
String myName = "Jon Java";
bike = new Bicycle( );
bike.setOwnerName(myName);
acct = new Account( );
acct.setOwnerName(myName);
acct.setInitialBalance(250.00);
acct.add(25.00);
acct.deduct(50);
//Output some information
System.out.println(bike.getOwnerName() + " owns a bicycle and");
System.out.println("has $ " + acct.getCurrentBalance() +
" left in the bank");
}
}
The Account Class
class Account {
private String ownerName; public void setInitialBalance
(double bal) {
private double balance;
balance = bal;
public Account( ) { }
ownerName = "Unassigned";
balance = 0.0; public void setOwnerName
} (String name) {
public void add(double amt) { ownerName = name;
balance = balance + amt; }
} }
public void deduct(double amt) {
balance = balance - amt;
}
public double getCurrentBalance( ) {
return balance;
}
public String getOwnerName( ) {
return ownerName;
}
Page 1 Page 2
The Program Structure for
SecondMain
Bicycle
SecondMain
Account
SecondMain.java Bicycle.java Account.java
To run the program: 1. javac Bicycle.java (compile) Note: You only
need to compile
2. javac Account.java (compile) the class once.
2. javac SecondMain.java (compile) Recompile only
3. java SecondMain (run) when you made
changes in the
code.
Quick Check!
• What is the output from the following code fragment?
Account acct;
acct = new Account( );
acct.setInitialBalance(250);
acct.add(20);
System.out.println("Balance: “ +
acct.getCurrentBalance());
• Write a code fragment to declare and create two
Account objects named acc1 and acct2. Initialize the
balance to $300 and $500, respectively.
Discussions: Design of Home Automation
System
Jamie and Kelly own a digital shower. They can give instructions to
the shower from any room or even via their smartphones. The home
automation system has state-of-the-art technology for voice and
face recognition, so can recognize that it’s Jamie when he calls in at
3.00 am on the way home from a hackathon and says: “gimme a hot
shower in 5 minutes”. It knows that “hot shower” for Jamie is a
different temperature than a “hot shower” for Kelly. The system can
play appropriate music in the shower, and knows what are Kelly’s
current hot favourites on her MP3 Player.
Here are some questions:
1. What are the important classes that the home automation
system needs to know about?
2. What methods will objects of those classes need to make
available to the system?
More concepts..
Basic Principles of Object
Orientation
Object Orientation
Encapsulation
Abstraction
Modularity
Hierarchy
What Is Abstraction?
◦ The essential characteristics of an
entity that distinguishes it from all
other kinds of entities.
◦ Defines a boundary relative to the
perspective of the viewer.
◦ Is not a concrete manifestation,
denotes the ideal essence of
something.
Example: Abstraction
Student Professor
Course Offering (9:00 a.m.,
Monday-Wednesday-Friday)
Course (e.g. Algebra)
What Is Encapsulation?
Hides implementation from clients.
▪ Clients depend on interface.
Improves Resiliency
Encapsulation Illustrated
Professor Clark
Professor Clark needs to be able
to teach four classes in the next
semester.
Name: J Clark
Employee ID: 567138
SetMaxLoad(4)
HireDate: 07/25/1991
Status: Tenured
TakeSabbatical()
Discipline: Finance
MaxLoad:3
What Is Modularity?
Breaks up something complex into manageable pieces.
Helps people understand complex systems.
Example: Modularity
For example, break complex systems into Billing
smaller modules. System
Course
Catalog
System
Course Registration
System Student
Management
System
What Is Hierarchy?
Increasing Asset
abstraction
BankAccount Security RealEstate
Decreasing Savings Checking Stock Bond
abstraction
Elements at the same level of the hierarchy
should be at the same level of abstraction.
What Is Polymorphism?
The ability to hide many different
implementations behind a single interface.
Manufacturer B
Manufacturer A Manufacturer C
OO Principle:
Encapsulation
Remote Control
Example: Polymorphism
financialInstrument.getCurrentValue()
Stock Bond Mutual Fund
What Is Generalization?
A relationship among classes where one class shares the
structure and/or behavior of one or more classes.
Defines a hierarchy of abstractions in which a subclass
inherits from one or more superclasses.
◦ Single inheritance.
◦ Multiple inheritance.
Is an “is a kind of” relationship.
