Advanced Programming with C#

IUST

Fall 2018

Object Oriented Programming

TOC

  • Object oriented programming concepts
  • Class, Object, Property and Method.
  • Interfaces
  • Encapsulation concepts
  • Implement and use first class in C#
  • Instantiate object
  • Status of object in memory
  • Garbage collector
  • Parameter passing
  • Different parts of memory

Object oriented programming

History of programming language

  • Machine language
  • Assembly: Naming for numeric machine language commands
  • High level languages:
    • such as C, Basic, Fortran
    • Structures closer to human language
      • such as loop, condition etc.
    • From the machine and assembly language are higher levels
    • This approach was a great advance

But the developer must still think of computer structures (even with a high level language)

It is better for the programmer to think about the problem structure than the structure of the computer

Problem space and solution space

Programming = Creating a software solution for a real issue

● Example: Software for managing books and members in a library

 Problem space

  • The space in which there is a problem: like a library
  • The components of space of library problem : book, member, shelf and ...

Solution Space

  • The space in which the solution is created: a C# program for managing the library
  • Library space solution components: project, program, variable, function

Programming = An attempt to map the problem space and solution space

Object Oriented Approach

  •  Think about the library's problem:
  •  What are the elements of your program?
  •  We think about functions and variables ...

Objects in Library Problem:

A book,

A member

A shelf and ...

Object Oriented Approach

  • Allows the programmer to display the elements of the problem space
  • Use the concepts and terminology of the same problem in the program that it writes

Object:

entities that are in the space of the problem and in the solution space (programs) are also seen

Object Oriented Programming

  • We write programs that match the language of the problem space
    • The same problem with the help of adding new data types for objects
    • Types of data are not limited to what the language provides
    • In addition to simple types (such as "shelf" and "book" type int and char
  • When you read the program, you see words that have meaning in the problem
  • A book, a member, the barrow of a book to a member, and ...
  • This abstraction makes language very flexible and powerful

Object Oriented languages

  • Smalltalk
    • One of the first successful object-oriented languages
    • One of the languages that inspired Java
  • C++
  • C#
  • Java
  • Scala
  • Python

Object Oriented VS procedural approach

Object-Oriented Programming Elements: Objects + Message Exchange between Objects

Procedural programming elements: functions + variables + function call

  • The Difference Between Thinking at Programming Time:

  • Thinking about objects and the relationship between objects: the object-oriented method

  • Thinking about memory, computer structure and ...: procedural approach

Object-Oriented Programming Specs

Object-oriented programming summarizes in five main features: "Allan Key"

  1. Everything is an object
  2. A program is a set of objects
    • By sending messages together,
    • Tell each other what to do
  3. Each object has its own memory
    • Which is made of other objects
    • (Object mode)

4. Each object has one type

5. All objects of a particular type can receive similar messages

Description of the booch from the object

An object consisting of status, behavior, and identity

Booch has added a description of "identity".

Each object has its own characteristics That state determines the object

For example: A library member has features such as name, age, etc.

Each object has methods It shows behaviors

For example: behavior "borrowing the book" for the object "Member"

And each object is unique: it has a distinct identity

even if there are two objects have the same "status" 

have unique address in memory

Class, Object, Property and Method

Object:

Existing objects in the problem space

Library:

Member  Mr."Ali Alavi", "Shahnameh" Book.

Football game:

Ali Karimi, Farhad Majidi, Azadi Stadium, Ball

Banking Program:

Maryam Alavi (customer), Azadi Branch

Class

Type, category, or batch of objects that have similar "Behavior" and "Attributes"  

Each class has several instances

  • Library: Book, member, shelf
  •  Play football: player, team, stadium
  • Banking program: customer, branch, account

Each class defines behavior and attributes (Property)

Any object in this class has these features and behaviors

  • Example: Member of the library

Features: Name, age, occupation

Behaviors: borrowing books

Light lt = new Light();
lt.On();

UML class diagram for light bulb

UML class diagram of person

Person personl = new Person();
personl.Name = "Taghi Taghavi";
personl.PhoneNumber = 66166601;
personl.ShowInformation();
Person
-name : String
-PhoneNumber : int
+ ShowInformation() : void
+ Name.set() : void
+ Name.get() : String
+ PhoneNumber.set() : void
+ PhoneNumber.get() : String

Access control

In class design: we can limit access to parts of the class
● Public and private in class

  • The class user can only use its public section
  • The general shows the interface class
  • Private sections inside the same class can be use. But they are not necessarily used by other classes

● Private sections are hidden from the viewers (implementation hiding)

Encapsulation

Encapsulation: defining features and behaviors + hiding implementation

  • Definition of a concept in the problem space in the form of a class of objects
  • Define new classes with public interfaces and hidden implementations
  • Encapsulation: Definition of type (class) + Definition of class interface (How to use the class)
  • The class will be Black Box. It can only be used in a particular way
  • Many commercial products are confined
    • TV, mobile phone, ...

Why encapsulation?

  • Operation and easier use
    • The user involved in the details will not be implemented
  • The open source may lead to misuse
    • Hiding the implementation will reduce the error rate
  • This design is more beautiful

Interface

  • Each object can exhibit certain behaviors
    • Ask for specific requests
  • Object Interface:
  • A set of behaviors for a callable object
    • Part of the class interface is "borrowed", for example
      • Each book has a lending behavior
      •  Example: Behavior It will be called "Shahnameh" for the book "to be borrowed"
  • The interface of each object in the class (type) is specified

Implement and use first class in C#

// Class Declaration
public class Dog
    {
        private String name;

        public void SetName(String n)
        {
            name = n;
        }

        public void Bark()
        {
            Console.WriteLine("Hop! Hop!");
        }
    }

Using Class


// Object Creation, Instantiation
Dog d = new Dog();

// Change state of object
d.SetName("Fido");

// Message passing
d.Bark();

What is variable "d"?

A reference to the object.

Use an Object

Person p = new Person();
p.SetName("Ali Hosseini");
Book b1 = new Book();
b1.SetTitle("Shahname");
p.Borrow(b1);
String s = p.name;
p.Age = 22;

Dot

  • Before a dot, the object name comes
  • usually after a dot, a method is called
  • After the dot, one of the features of the object may come
  • Provided that it is available. For example, public

Objects on program

Dog d1 = new Dog();
d1.Name = "Belle";
d1.Age = 3;
Dog d2 = new Dog();
d2.Name = "Fido";
d2.Age = 4;
Belle
3
Fido
4

Objects in memory

Reminder:

Every object has a state, behavior, and identity

  • Each object is placed in memory
    • Memory Content = Object state
    • Object address in memory ≈ Object identity
    • Object behavior: Defined in object class already

new operator

  • Creates a new object of the specified class
  • Returns the reference to the constructed object
  • The new operator creates a memory in a part named Heap 
String s = new String();
Dog d = new Dog();
Rectangle r = new Rectangle();
StreamReader sr = new StreamReader();

Data types

  1. Primitive Data Types :
    • byte, short, int, long, float, double, bool, char
    • There are some limited and distinct data types available in C#
    • Each variable of these types contains a value (not an object)
  2. ​Reference Data Types:
    • Like String, StreamReader, Dog or Book
    • Some (like String) are available in the language and we define and some others (like Book)
    • Each variable of these types is referenced to an object

The difference between a primitive variable (with an object)

  • Primitive types do not have the ability to use new operator
  • Not referenced
  • Hold a value instead of keeping referencing an object
  • They do not have the option to use dot
  • Because they are not objects that have a feature or behavior
new int(); //ERROR
int a = 5;
a.value = 6; //ERROR

Reference to a object

  • Referral is a concept as a pointer
  • A somewhat similar point in the C ++ language
  • When defining a variable, you actually create a referral, not an object

 

 

 

 

  • Exception:
    • Variables of the primary data types
    • These variables do not refer to an object, they hold the value themselves

Making objects

  • This code does not create a new object:
  • Only one referral, which still does not refer to an object
  • You can not use the str variable at this time
  • The value of the str variable is empty (null)
  • NULL value: A reference that does not refer to an object
  • Each variable (referral), must be connected to a real object (unless it is primitive) 
    • For example, with the new operator, point to a new object
    • Or a non-empty variable inside it (with the = )
String str;
str= new String(); //Refer to new object
str= name; //Refer object

The effect of the assignment operator (equal to one reference)

String name = new String("Ali");

Ali

name

name

Ali

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