Introduction to Objects

1
Introduction to Objects

• What are Objects?
• The Three Keys to Object Technology
• Definitions

2
What are Objects ?

• To a child they are something perceptible by one
  or more of the senses.
• To a CIS professional they are a software packets
  that abstract important features of a real object.

3
What are Objects ?

• Real objects are such things as
• Porsche

4
What are Objects ?

• Real objects are such things as
• Los Angeles

5
What are Objects ?

• Real objects are such things as
• Alan Kay (Customer)

6
What are Objects ?

• Real objects are such things as
• Versateller

7
What are Objects ?

• Real objects are such things as
• 1. Things Porsche
• 2. Places Los Angeles
• 3. Roles Alan Kay
• 4. Systems Versateller

8
What are Objects ?

• Real objects have characteristics
• 1. Porches Top Speed
• 2. Los Angeles Population
• 3. Customers Balanced Owed
• 4. Versatellers Amount on Hand

9
What are Objects ?

• Real objects also have behaviors
• 1. Porches Accelerate
• 2. Los Angeles Tax
• 3. Customers Purchase
• 4. Versatellers Dispense Cash

10
What are Objects ?

• Porsche - Top Speed, Accelerate
• Los Angeles - Population, Tax
• Alan Kay - Amount Owed, Purchase
• Versateller - Amount on Hand, Dispense Cash

11
What are Objects ?

• The Three Keys to Object Technology
• Key 1 A software object has both characteristics
  and behavior encapsulated in it.
• Key2 Software objects communicate by messages.
• Key 3 Software objects can inherit
  characteristics and behavior just like many real
  objects.

12
The Three Keys to Object Technology

• Key one
• Characteristics are
• encapsulated
• by the objects
• behavior

Location
Call Bank
13
The Three Keys to Object Technology

• Key two
• Objects communicate by messages

14
The Three Keys to Object Technology

• Key two (also)
• Messages are polymorphic (mean different things
  to different objects)
• Open Drawing Window
• Open Graphics Window
• (Polymorphism means different implementations
  can be hidden behind a common interface)

15
The Three Keys to Object Technology

• Key three
• Objects can be classified into classes
• Classes are a template that is used manufacture
  objects (instances)
• (Note that instance is a synonym of object)

16
The Three Keys to Object Technology

• Key three (also)
• Classes contain the
• behavior called methods
• while the instances
• contain the
• characteristics called
• variables

17
The Three Keys to Object Technology

• Key three (also)
• Each class can
• inherit both
• variables and
• methods

18
The Three Keys to Object Technology

• Key three (also)
• Methods and variables
• can override their parents
• (CD Deposit overrides
• Account Deposit)

19
Definitions

• Object
• A software packet that abstracts the salient
  behavior and characteristics of a real object
  into a software package that simulates the real
  object.

20
Definitions

• Encapsulation
• The containment of the data behind a software
  membrane consisting of methods. The data can
  only be accessed through the encapsulated
  behavior.

21
Definitions

• Message
• A signal from a client object requesting
  services from a server object.
• The message may contain arguments.
• The server object may return a response.

22
Definitions

• Class
• A template for defining new object instances.
• It is sometimes called an object class.
• The methods reside in the class object.

23
Definitions

• Instance
• A term used to refer to an actual object.
• Sometimes called an object instance.

24
Definitions

• Inheritance
• A technique to allow classes to use a parent
  classes methods and data.
• Inheritance can have many levels

25
Definitions

• Polymorphism
• A request handling mechanism that selects a
  method depending on the message and the target
  object.
• Thus the message means different things to
  different objects.

26
Definitions

• Overriding
• Where an overloaded method is chosen from the
  child class instead of from the parent class.

27
Definitions

• Method
• The actual computer code that is encapsulated in
  the object class.

28
Definitions

• Subclass
• A class that has a parent class to inherit from.

29
Summary

• Object technology is the current modern paradigm
• OO can enable reuse of system design and coding
  effort (and consequently save a lot of time and
  money)
• Systems built with object technology should be
  able to be built faster, be more reliable, and be
  more maintainable
• Use of object technology requires a different way
  of thinking than does traditional programming