Overview of Object-Oriented Software Design and Java Programming potx

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Overview of
Object-Oriented Software
Design and Java Programming
Putting the Pieces Together!
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Object-Oriented Design
A technique for developing a
program in which the solution
is expressed in terms of
objects self- contained
entities composed of data and
operations on that data.
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Object Oriented Programming
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Programmer thinks about and
defines the attributes and behavior of
objects.
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Often the objects are modeled after
real-world entities.
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Very different approach than
function-based programming (like C).
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Reasons for OOP
Abstraction
Polymorphism
Inheritance
Encapsulation

Software Engineering Issues
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Objects to Classes
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A class defines the pattern used when
instantiating an object of that type.
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A class generally contains private data and
public operations (called methods).
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Class: Object Types
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A Java class is an object type.
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When you create the definition of a
class you are defining the attributes and
behavior of a new type.
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Attributes are data members.
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Behavior is defined by methods.
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Creating an object
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Defining a class does not result in
creation of an object.
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Declaring a variable of a class type
creates an object. You can have many
variables of the same type (class).

Instantiation
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Superclass and Subclass
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Inheritance enables us to define a new class
(called a subclass) that inherits the properties of
an already existing class.
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The newly derived class is then specialized by
adding properties specific to it.
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The class being inherited from is the superclass.
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The class that inherits properties is the subclass.
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Defining Objects
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An object-oriented program consists of
many objects.
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An object is composed of identity, state
(attributes, data, and their current values)
and behavior (operations) .
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Identity, State, Behavior
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Identity is the property of an object that
distinguishes it from all other objects.
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The failure to recognize the difference

between the name of the object and the
object itself is the source of many errors
in object-oriented (OO) programming.
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Identity, S ta te, Behavior
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The state of an object encompasses all of the
(static) properties of the object plus the current
(dynamic) values of each of these properties
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A property is an inherent or distinctive
characteristic, trait, quality, or feature that
contribute to making an object uniquely that
object
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We will use the word attribute, or data
member, to refer to the state of an object
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Examples of State
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Properties
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Elevators travel up or down
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Vending machines accept coins
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Clocks indicate the current time
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Values
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Current floor
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Number of coins deposited
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The number of minutes since the last
hour
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Identity, State, Behavior
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Behavior is how an object acts and reacts,
in terms of state changes and interactions
with other objects.
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An operation is some action that one
object performs upon another in order to
elicit a reaction.
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We will use the word method to describe
object behavior in C++.
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Invoking a method causes the behavior to
take place.
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Classes
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Classes are the definitions (or
blueprints) used to create objects. I’d
say: descriptions of objects.
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To make a car the manufacturer must

first have a design from which to build
the first car. Then, once all the problems
are worked out, the design is used to
build all the cars of that model.
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Objects
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An object is an instance of a class.
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If we have a class definition called Car,
then we can think of Audi, BMW, and
Corvette as each being an instance
(object) of the class Car, i.e., they are
each a type of car.
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Object example
Audi 6 BMW Z3 Corvette
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Notice that all objects are of the same type. All objects
are cars!
Car Car Car
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Classes and Objects
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An object is an instance of exactly one class
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Corvette can not be an instance of a car class
and an instance of a plane class at the same
time.
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An instance of a class, an object, belongs to
that particular class.
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A Corvette is a car ⇒ Corvette belongs to the
class Car.
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Classes
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Once a class is defined you can create as
many instances of the class (objects from
the class) as you would like.
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Once a blue print is completed for the 2004
Porsche 911, Porsche will use an assembly
line to build as many instances of the 2004
Porsche 911 as they wish.
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Defining a class
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Properties are variables which describe the
essential characteristics of an object.
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Properties of a car: color, model, make, how many
doors, transmission type, direction of movement, etc.
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Behaviors are methods that describe how the
object behaves and how the properties may be
modified.
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Behavior of a car: braking, changing gears, opening

doors, moving forwards or backwards, etc.
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Instance variables
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The class definition will include parameter definitions
(properties) that represent data about a particular object,
instance variables.
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Example, Joe's car may have 4 gallons of gas in it while
John's car has 10 gallons.
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The amount of gas in each car may change without
affecting the amount of gas in the any other cars.
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All instances (objects) of a class will have a set of instance
variables that are specific to that individual object.
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The combination of the values of these instance variables
is known as the object’s state.
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Instance variables
Audi 6 BMW Z3 Corvette
Car Car Car
Car
MaxSpeed = 155 MaxSpeed = 165 MaxSpeed = 145
MaxSpeed
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Class variables
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The class definitions may also include

parameter definitions that represent data that
is shared by all class instances (objects),
called class variables.
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In the case of the car class, we will define a
maximum allowed speed, by the law
(variable MaxSpeed). This will be the same
for each individual car.
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Class variables
Audi 6 BMW Z3 Corvette
Car Car Car
Car
MaxSpeed = 155 MaxSpeed = 165 MaxSpeed = 145
MaxSpeed
MaxSpeed=155
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Class variables
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Class variables may also be used to
keep track of things such as how many
instances of a class exist.
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Example: let’s create a counter the
records how many cars are in the
garage.
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Class variables
Audi 6 BMW Z3 Corvette
Car Car Car

Car
MaxSpeed = 155 MaxSpeed = 165 MaxSpeed = 145
MaxSpeed
MaxSpeed=155
NumCars = 3