Object-oriented Analysis, Design & Programming

Object-oriented Analysis,
Design & Programming
Allan Spartacus Mangune

Delivery
• Lectures – 2.5 hours
• 2 case studies and exercises – 30 minutes each

Agenda
Object-oriented Analysis
Object-oriented Design
Object-oriented Programming

Object-oriented Analysis
Best done in iterative and incremental approach
• Refine as you learn more about the system and implementation constraints
Develop the models of the system based on functional requirements
• Does factor implementation constraints of the system into the model
Organize requirement items around objects that interact with one another
• Requirement items are mapped to the real things of the system
• Each item may be defined as object with data and behavior

Process
Model the system of its intended use taking into account the description and
behavior of each object
• Emphasize on what the system does
Define how objects interact with one another
Commonly used process tools
• Use case
• Conceptual models (also referred to Domain Models)

Use Case
Source:
http://en.wikipedia.org/wiki/File:Use_case_restaurant
_model.svg
A sequence of related actions to accomplish a specific goal
Each role in the system is represented as actor
The actor can be a human or other systems
• Identify the main task of each actor
• Read
• Write/Update
• Notification of effects of action taken on internal and/or external system

Conceptual Models
Abstract ideas in problem domain
Describes the each object of the system,
its behavior and how objects interact with
one another
• Attributes, behaviors and constraints
Use this model to build the vocabulary of
concepts and validate your understanding
of problem domain with domain experts
• Defer encapsulation details to the design phase
Source: http://en.wikipedia.org/wiki/File:Domain_model.png

Object-oriented Design
System
planning
process
Solve specific
problem
Promotes
correct
program flow

Starting the Design Phase
Can be started in parallel with analysis phase
• Incremental approach is preferred
Use the artifacts in analysis phase as inputs
• Use case models
• Conceptual models

Key Concepts of Object-oriented Design
Objects and
Classes
Encapsulation
and Information
Hiding
Inheritance
Polymorphism Interface

Objects
The most basic elements in object-oriented design
An object represents a real entity with attributes and behaviors
• Has a unique identity in the system
Objects interactions
• Interface is defined to describe all the actions an object must perform

Class
Represents the blue-print of an object
• An object that is created based on a class is called an instance of
that class
Contains attributes, data and behaviors that act on
the data
Defines the initial state of data
May contain interface that defines how the class
interact with the other parts of the system
• For this purpose, an interface is a set of methods and properties
exposed through public access modifier

Encapsulation and Information Hiding
The internals of an object is hidden
• Restricting access to its data
Prevents external code from setting the data in invalid state
Access to the data can be provided indirectly through public properties and methods
Reduces complexity of the system

Inheritance
When a class derives from another class
• The class that inherits from a based class is called
inheriting class or subclass
Promotes code reuse
• Base class inherits all of the base class operations, unless
overridden
Subclass may define its own implementation
of any of the operations of the base class

Polymorphism
Ability of the inheriting class to change one
or more behaviors of its base class
• This allows the derived class to share the
functionality of the base class

Interface
An abstract class that contains methods
without implementations
• Defines the rules for method signature and return type
• Implementation is deferred to the class the implements
the interface
Enforces rules to one or more classes that
implement the interface

Object-oriented Programming
Classes and
Objects
Access
Modifiers
Member Fields
and Properties
Methods
Inheritance Polymorphism Interface

Access Modifiers
public
• The type or member can be accessed by any other code in
the same assembly or another assembly that references it.
private
• The type or member can only be accessed by code in the
same class.
protected
• The type or member can only be accessed by code in the
same class or in a derived class.
internal
• The type or member can be accessed by any code in the
same assembly, but not from another assembly.
protected internal
• The type or member can be accessed by any code in the
same assembly, or by any derived class in another assembly
Source: http://msdn.microsoft.com/en-
us/library/dd460654.aspx#Interfaces

Classes and Objects
A class describes the object
An object in an instance of a class
• An object is instantiated through the
constructor of the class
public class Customer
{
public Customer() {}
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Customer Add()
{
return ….
}
}
Customer customer = new Customer()

Member Fields and Properties
Local variables that must be private to the class
• Holds the data of the class
External access to the fields are usually
provided through public Properties
{
private int id;
private string firstName;
private string lastName;
public int Id {
get { return id; }
set { id = value; }
}
public string FirstName { … }
public string LastName { … }
}
customer.FirstName = “Allan Spartacus”

Methods
Defines the behaviors of the class
May or may not return a type
• void – no return type
Can be overloaded
• The signature of each method must be
unique
{
…
public Customer Add () { … }
public Customer Add(Customer customer){ … }
public Customer Edit () { … }
public bool Delete(int id) { … }
private void ConcatName(){ … }
}
customer.Add();
customer.ConcatName();

Inheritance
Enables a new class to reuse, extend and
change the behavior of a base class.
• All classes written in C# implicitly inherits from
System.Object class
• A C# class can only inherit from a single base class
public class Person {
public int Id { get; set; }
public string FirstName { get; set; }
}
public class Customer : Person {
public string CompanyName { get; set; }
}
public class Employee : Person {
public string EmployeeNumber { get; set; }
}
Employee employee = new Employee();
employee.Id = 1;
employee.FirstName = “Allan Spartacus”;
employee.EmployeeNumber = “GF4532”;

Sealed Class
To prevent a class from inheriting
from, define it as a sealed class
public sealed class Vendor : Person {
public string CompanyName { get; set; }
}
public class InternationaVendor : Vendor {
}

Abstract Class
When a class is intended as a base class that
cannot be instantiated, define it as abstract class
• Multiple derived classes can share the definition of an
abstract class
An abstract class can be used as interface by
defining abstract methods
• Abstract methods do not have implementation code
• Implementation code is defined in the derived class
public abstract class Manufacturer {}
Manufacturer manufacturer = new Manufacturer()
public abstract class Item {
public abstract void Add();
}
public class Product : Item {
public override void Add() {
….
}
}
public class Service : Item {
public override void Add() {
….
}
}

Interface
A collection of functionalities that can be implemented by
a class or struct
While a class is limited to inherit from a single base class, it
can implement multiple interfaces
A class that implements an interface must define methods
that have similar signatures defined in the interface
interface class IItem {
void Add();
}
public abstract class Product : IItem {
public void Add() {
….
}
}
public class Service : IItem {
public void Add() {
….
}
}

References
Object-oriented analysis -http://www.umsl.edu/~sauterv/analysis/488_f01_papers/wang.htm
http://en.wikipedia.org/wiki/Use_cases
Object-oriented design - http://en.wikipedia.org/wiki/Object-oriented_design
Object - http://en.wikipedia.org/wiki/Object-oriented_programming
Encapsulation and data hiding - http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)
Polymorphism - http://en.wikipedia.org/wiki/Object-oriented_programming
Interface - http://en.wikipedia.org/wiki/Object-oriented_programming
Inheritance - http://en.wikipedia.org/wiki/Object-oriented_programming

Copyright (C) 2014. Allan Spartacus Mangune
This work is licensed under a Creative Commons Attribution-
NonCommercial-ShareAlike 4.0 International License.
License URL: http://creativecommons.org/licenses/by-nc-
sa/4.0/

Object-oriented Analysis, Design & Programming

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