Programming

1
Programming At Its Infancy

• A program is a single block of procedural code
• Disadvantages
• Reusability is practically nil.
• Programming Complexity is high.
• Software cannot not evolve gracefully as changes
  in one part of the software can have unwanted
  side-effects.

2
Programming The Structured Approach

• Top-down design followed by bottom-up programming
• Top-down decomposition driven by functional
  criteria
• Architecture reflects system functions

3
The Structured Approach Advantages

• Modularization implies
• Reduction in software complexity
• Increased reusability
• Reduction in unwanted side-effects as much of the
  effect is confined to the module being changed.

4
The Structured Approach Disadvantages

• Produces satisfactory results only when functions
  have been identified properly and remain
  unchanged through time.
• Software structure is induced by functions. Thus
  evolution of these functions may imply important
  structural modifications.
• Guarantees only limited modularizations thereby
  rendering subsequent modifications difficult and
  wrought with side-effects.

5
Programming The Object Oriented Approach

• A paradigm shift from a function-centric approach
  to an object-centric approach to software
  development.
• Structure induced by players (which constitute
  the more static part of the system) rather than
  by functions (the dynamic and evolving part of
  the system).
• Doesnt replace the structured approach builds
  on top of it.
• Further modularization achieved through the
  decoupling of the system into independent objects.

6
The Object Oriented Approach Advantages

• Models the real world more closely.
• Is easier to maintain because its structure is
  inherently decoupled.
• Leads to reuse which in turn leads to faster
  software development and higher quality programs.

7
What are objects anyway

• Objects in an object oriented system are models
  or abstractions of the things that make up the
  real-world system.
• Objects may correspond to actual physical objects
  such as car, table,employee, customer and so on.
• Objects may also correspond to concepts such as a
  bank account, insurance policy etc.

8
Objects

• They have properties much like real world
  objects. Eg. A car object may have properties
  colour, make, price etc.
• They exhibit behaviour much like physical
  objects. Eg. A car object can move, accelerate.

9
Object Defined

• An object is a complex data type that contains
• other data types, usually called properties,
  attributes or variables, and
• modules of code, usually called operations or
  methods that manage these attributes.

10
Abstraction

• Abstraction maps real-world objects to computer
  models

Id No Make Model Colour Year of Manufacture
Employee Code Name Designation Basic Pay Division
11
Encapsulation
Attributes
Operations
Quote Price
Customer
Price?
Price
Check Price
Salesperson
Product
12
Encapsulation

• Encapsulation means objects dont know or care
  how other objects store or process data.
• The hiding of implementation details is referred
  to as encapsulation.

13
Encapsulation Advantages

• Leads to a higher level of modularization in the
  sense that
• each object is independent of every other object
  and
• the procedural code contained in each object is
  modularized into several independent operations.

14

• Data is encapsulated in objects
• Data protected against unexpected accesses thus
  guaranteeing data integrity

15

• Changes to internal data structures or
  operations of an object affect only that object.
  
• Information hiding and reduced impact of side
  effects associated with change
  

16

• Methods or operations manipulate a limited no. of
  attributes
• They are cohesive

17

• Communication occurs only through the methods
  that comprise the wall
• Object is decoupled from other elements of the
  system

18

• All the necessary data structures and functions
  for a particular object are contained within the
  object
• Increased reusability

19

• Encapsulation
• High-Quality Software

20
Objects, Classes and Instances

• Can you build completely separate objects for
  each variation of every object in our world?
• No

21
Objects, Classes and Instances

• Employees of an Organization

Employee Code Name Designation Basic Pay Division
395 Tom SSA 10,000 XYZ
Employee Code Name Designation Basic Pay Division
1360 Lara SA 7,000 ABC
Employee Code Name Designation Basic Pay Division
2375 Dick PSA 15,000 XYZ
22
Objects, Classes and Instances

• A class is a generalized description (e.g. a
  template, blueprint) that describes a collection
  of similar objects.

Object Chair1
Class Chair
The object inherits all attributes operations
of the class
Cost Dimensions Weight Location Color
Cost Dimensions Weight Location Color
Buy Sell Weigh Move
Buy Sell Weigh Move
23
Objects, Classes and Instances

• Each object belongs to a class.
• An object has values associated with its
  attributes.
• Software objects are built from the class via a
  process referred to as instantiation. Any object
  is an instance of a class.
• At run time, a single class like employee can
  have hundreds of objects in existence at the same
  time.

24
Object-oriented Decomposition
Attributes
Operations
Quote Price
Customer
Price?
Price
Check Price
Salesperson
Product
25
Object Intercommunication

• Decomposition is not the end of the development
  of an object oriented system it signals the
  beginning.
• The objects have to be tied together to allow an
  applications functionality to be built .

26
Object Intercommunication

• In an object-oriented system, teams of objects
  operate in synergy to implement the functionality
  of the application. At execution time, the
  objects contribute as a whole to the proper
  execution of the application.

27
Object Intercommunication

• And how do they do this?

28
What is a message?

• Messages are the means by which objects interact.
• Messages tie an object oriented system together.
• Message is a dynamic integrator that allows an
  application to built through the collaboration of
  a group of objects.
• Message dynamically links the objects that were
  separated by the decomposition process.

29
Message Defined

• The unit of inter-object communication is called
  message.

30
Inheritance

• More General Abstractions

Vehicle
Is a
Is a
Land Vehicle
Air Vehicle
Is a
Is a
Is a
Is a
Car
Truck
Plane
Helicopter
31
Class Inheritance Specialization
ClassA
Attribute A1
Operation A1
ClassB
Attribute A1 Attribute B1
Inheritance
Operation A1 Operation B1
ClassC
Attribute A1 Attribute B1 Attribute C1
Operation A1 Operation B1( B1 code
modified) Operation C1
Specialization
32
Inheritance How to implement

• Generalization achieved through abstraction.
• Specialization achieved through extension.
• Generally implemented at the same time.

33
Generalization Specialization
Vehicle
Generalization
Specialization
Land Vehicle
Air Vehicle
Car
Truck
Plane
Helicopter
34
Inheritance Advantages
Inheritance
Better management of Complexity
Code Reuse
Faster Development simplified maintenance
35
An example
Vehicle
Move
Land Vehicle
Air Vehicle
Move
Move
Plane
Car
Truck
Helicopter
Move
Move
Move
Move
36
Polymorphism

• The ability to trigger different operations in
  response to the same message is called
  polymorphism.
• This means that the same message can behave in
  different ways depending on what object it is
  sent to.

37
Polymorphism

• Polymorphism is achieved by writing code , not in
  terms of the sub-classes, but in terms of the
  super class.
• The benefits of polymorphism are mainly obtained
  during maintenance.

38
The Software Problem

• Growing demand for sophisticated software
• Growing software complexity

39
What is UML?

• UML stands for Unified Modeling Language
• UML is a universl language for object-oriented
  modeling
• UML is the standard language for visualizing,
  specifying, constructing and documenting the
  artifacts of a software system
• Maps real-world processes of a computer system
  with a graphical representation or blue print.

40
Benefits of UML

• Helps capture business processes
• Enhances communications
• Manages complexity
• Defines architecture
• Enables reuse

41
UML Diagrams

• Five different groups of UML diagrams offer five
  different ways of looking at the same problem
• Use Case Diagrams
• Use Case Diagrams
• Use Case Descriptions
• Static Structure Diagrams
• Class Diagrams
• Object Diagrams

42
UML Diagrams

• Interaction Diagrams
• Sequence Diagrams
• Collaboration Diagrams
• State Diagrams
• State Diagrams
• Activity Diagrams
• Implemetation Diagrams
• Component Diagrams
• Deployment Diagrams

43
The UML Use Case Diagrams

• Represent the functions of a system from a users
  point of view.
• They allow the definition of the systems
  boundary and the relationships between the system
  and the environment.

44
The UML Static Structure Diagrams

• The class diagram shows the classes that will be
  included in your application and the
  relationships between classes.
• Object diagrams are used to explore specific
  problems with specific classes.

45
The UML Interaction Diagrams

• Sequence Diagrams show the flow of messages
  (events) between objects in a temporal context.
• Collaboration Diagrams are a combination of
  object and sequence diagrams. They show the flow
  of events between objects.

46
The UML State Diagrams

• A state diagram shows all of the values (states)
  that the attribute of an object can take as
  messages (events) are processed. State diagrams
  are only prepared for classes whose instances are
  very dynamic.
• An activity diagram represents the internal
  behaviour of a method or a use case as a sequence
  of steps.

47
The Solution

• Software engineers must know
• How to do their job
• How to explain their work to others and
• How to understandothers work, when it is
  explained to them

48
The UML Implementation Diagrams

• Implementation diagrams show design and
  architectural decisions.
• Component Diagrams describe software components
  and their relationships within the implementation
  environment they indicate the choices made at
  implementation time.

49
The UML Implementation Diagrams

• Deployment Diagrams show the physical layout of
  the various hardware component (nodes) that
  compose a system, as well as the distribution of
  executable programs (components) on this
  hardware. Placing component diagrams on top of
  deployment diagrams indicate which modules of
  code will go on which hardware platforms.