t4 - object oriented programming with c 2.0

7/31/2019 T4 - Object Oriented Programming With C 2.0

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C# and .NET Technology

Object OrientedProgramming with C# 2.0


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Objectives

Essentials of Object-OrientedProgramming

Classes and Objects

Using Encapsulation

C# and Object Orientation

Defining Object-Oriented Systems

The Object Hierarchy


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Objectives

Use Constructors In C#

Use Destructors In C#

Explain the working of Garbage Collector

Discuss Method Overloading

Discuss Operator Overloading

Use Inheritance in C#

Discuss Overriding


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Objectives

Discuss Polymorphism

Use Virtual Functions

Discuss relationship between polymorphism and

inheritance Discuss Abstract Base classes

Discuss the concept of Interfaces

Use Interfaces Discuss Properties

Discuss Indexers


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Object OrientedProgramming Overview


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1. Object Oriented ProgrammingHistory

Object-oriented programming has roots that can betraced to the 1960s:

As hardware and software became increasinglycomplex, quality was often compromised.

Researchers studied ways to maintain software qualityand developed object-oriented programming in part toaddress common problems by strongly emphasizingdiscrete, reusable units of programming logic.

The methodology focuses on data rather thanprocesses, with programs composed of self-sufficientmodules (objects) each containing all the informationneeded to manipulate its own data structure.


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1. Object Oriented ProgrammingHistory

The Object-Oriented methodology focuses on datarather than processes, with programs composed ofself-sufficient modules (objects) each containing all theinformation needed to manipulate its own data

structure. This is in contrast to the existing modular

programming which had been dominant for manyyears that focused on the functionof a module

An object-oriented program may thus be viewed as acollection of cooperating objects, as opposed to theconventional model, in which a program is seen as alist of tasks (subroutines) to perform
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2. OOP Fundamental Concepts

Fundamental Concepts in OOP are: Class Object Instance Method Message passing Inheritance Abstraction

Encapsulation Polymorphysm De-coupling


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I. Classes and Objects


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1. What is a class?

A class define the abstract characteristics of athing (object), including the thing'scharacteristics (its attributes, fields orproperties) and the thing's behaviors (thethings it can do, or methods, operations orfeatures).

For example, the class Dog would consist oftraits shared by all dogs, such as: Breed and fur color (characteristics), and

The ability to bark and sit (behaviors)
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An example: A class with its attributes,

fields, properties, methods,


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2.1. Compare Properties and PublicFields

Properties can be recognizeby IDEs (such as VisualStudio.NET) but public fields

Properties are the hybrid offields and methods

A property is like a clock-knob: when you turn it, the

hour hand and the minutehand and the second handare automatically adjusted


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2.2. Constructor

Whenever a class or struct is created, itsconstructor is called. A class or struct mayhave multiple constructors that take differentarguments.

Constructors enable the programmer to setdefault values, limit instantiation, and writecode that is flexible and easy to read.

If you do not provide a constructor for yourobject, C# will create one by default that

instantiates the object and sets membervariables to the default values Static classes and structs can also have

constructors
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2.3. Destructor

Destructors are used to destruct instances of classes. Destructors cannot be defined in structs. They are only used

with classes.

A class can only have one destructor.

Destructors cannot be inherited or overloaded.

Destructors cannot be called. They are invokedautomatically.

A destructor does not take modifiers or have parameters.

The destructor implicitly calls Finalize on the base class ofthe object.
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2.4. Indexers

Indexers allow you to index a class or astruct instance in the same way as anarray

An indexer is declared like a propertyexcept that the name of the member isthis followed by a parameter list written

between the delimiters [ and ]


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Indexer example

BEFORE


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Indexer example

NOW


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3. Access Modifiers

Access modifiers are keywords used to specify the declaredaccessibility of a member or a type. This section introduces the fouraccess modifiers: Public: The public keyword is an access modifier for types and type

members. Public access is the most permissive access level. There areno restrictions on accessing public members

Protected: The protected keyword is a member access modifier. A

protected member is accessible from within the class in which it isdeclared, and from within any class derived from the class that declaredthis member.

Internal: Internal members are accessible only within files in the sameassembly. A common use of internal access is in component-baseddevelopment because it enables a group of components to cooperate in aprivate manner without being exposed to the rest of the application code.

Private: The private keyword is a member access modifier. Privateaccess is the least permissive access level. Private members areaccessible only within the body of the class or the struct in which they aredeclared. Nested types in the same body can also access those privatemembers.
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partial class definition example


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4. What is an Object?

An Object is a pattern of a class.

Exp: The class of Dog defines all

possible dogs by listing thecharacteristics and behaviors they canhave; the object Lassie is one particular

dog, with particular versions of thecharacteristics. A Dog has fur; Lassiehas brown-and-white fur.


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7. static keyword example


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7. static keyword

The static modifier on a class means that the classcannot be instantiated, and that all of its members arestatic.

A static member has one version regardless of howmany instances of its enclosing type are created.

A constant is implicitly a static member.

A static member cannot be referenced through aninstance. Instead, it is referenced through the typename


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8. Nested Classes

A class defined within a class or struct iscalled a nested class
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Inheritance - Examples


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2. Single and Multiple inheritances

Single inheritance: deriving from onebase class

Multiple inheritance: deriving from two ormore base classes


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4. Operator Over-loading

Like C++, C# allows you to overload operatorsfor use on your own classes. This makes itpossible for a user-defined data type to look asnatural and be as logical to use as a

fundamental data type

To overload an operator, you write a functionthat has the name operator followed by thesymbol for the operator to be overloaded


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8. new keyword examples

In the following example, new keyword

is used as a modifier:


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9. Why use inheritances?

Enables a series of classes to be relatedtogether according to their commonparts:

common members only specified once, inbase class

can be accessed in objects of all classesderived from the base class

Increases efficiency of production andflexibility


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IV. Polymorphism


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1. What is the polymorphism?

Polymorphism is derived from two Greek words. Poly (meaningmany) and morph (meaning forms). Polymorphism means manyforms

Understanding Polymorphism is crucial to any OO languageprofessional , be it a Java , C++ or C# programmer

If a Dog is commanded to speak(), it may emit a bark, while if aPig is asked to speak(), it may respond with an oink. Both inheritspeak() from Animal, but their subclass methods override themethods of the superclass, known as overriding polymorphism

We implement polymorphism by using virtual and overridekeywords


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3. override and virtual keywords

override and virtual keywords are used toimplement polymorphism in C#.NET

The override modifier is required to extend ormodify the abstract or virtual implementation ofan inherited method, property, indexer, orevent

The virtual keyword is used to modify amethod, property, indexer, or event declarationand allow for it to be overridden in aderived class


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4. Why polymorphism?

Why include polymorphism in aprogramming language?

Because it significantly reducesprogramming effort. In particular,polymorphism allows you to write one

method for a variety of types, rather thanto write one method per type


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V. Abstractions:Abstract Base Classes &

Interfaces


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1. What is the abstraction?

Abstraction (from the Latin abs, meaning awayfromand trahere, meaning to draw) is theprocess of taking away or removing

characteristics from something in order toreduce it to a set of essential characteristics

In object-oriented programming, abstraction isone of three central principles (along with

encapsulation and inheritance)
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4 Why must make everything


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4. Why must make everythingabstract?

The importance of abstraction is derived fromits ability to hide irrelevant details and from theuse of names to reference objects.

Abstraction is essential in the construction ofprograms. It places the emphasis on what anobject is or does rather than how it isrepresented or how it works. Thus, it is the

primary means of managing complexity inlarge programs

5. Differences between Abstract


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5. Differences between AbstractClasses Vs. Interfaces

The biggest difference between anabstract class and an interface is: Aclass may implement an unlimited

number of interfaces, but may inheritfrom only one abstract

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