Object

Object
WHY SHOULD I USE OBJECT ORIENTED?
WHAT IS THE OBJECT?
PRINCIPLE OF OBJECT ORIENTED
INHERITANCE
ENCAPSULATION
ABSTRACTION
POLYMORPHISM

Why should i Use Object oriented?
Code Reuse and Recycling
Encapsulation (part 1): Once an Object is created, knowledge of its
implementation is not necessary for its use.
Encapsulation (part 2): Objects have the ability to hide certain parts of
themselves from programmers.
Design Benefits
Software Maintenance

Why not?
Size: Object Oriented programs are much larger than other programs.
Effort: Object Oriented programs require a lot of work to create.
Speed: Object Oriented programs are slower than other programs.

Object is Essence
What is the object?
anything you can "know" something about

How to find object?
▶ Everything that exists
▶ Understanding the objects properties or attributes.
▶ Understanding it's uses, behaviors or actions (methods).
▶ Anything written on paper
▶ In design a DB use Entity discovering method

Principle Of object oriented
Major Elements
▶ Encapsulation: We will learn to hide unnecessary details in our
classes and provide a clear and simple interface for working with
them.
▶ Inheritance: We will explain how class hierarchies improve code
readability and enable the reuse of functionality.
▶ Abstraction: We will learn how to work through abstractions: to deal
with objects considering their important characteristics and ignore
all other details.
▶ Polymorphism: We will explain how to work in the same manner with
different objects, which define a specific implementation of some
abstract behavior.

Principle Of object oriented
Minor Elements
▶ Typing: According to the theories of abstract data type, a type is a
characterization of a set of elements
▶ Concurrency: In an object-oriented environment, there are active
and inactive objects.
▶ Persistence: An object occupies a memory space and exists for a
particular period of time.

Inheritance
▶ Inheritance is one of the fundamental attributes of object-oriented
programming. It allows you to define a child class that reuses
(inherits), extends, or modifies the behavior of a parent class.
▶ C# is (single inheritance), unlike C++ which supports inheriting from
multiple classes (multiple inheritance).

▶ /// <summary>Felidae is latin for "cats"</summary>
▶ public class Felidae
▶ {
▶ private bool male;
▶ // This constructor calls another constructor
▶ public Felidae() : this(true)
▶ { }
▶ // This is the constructor that is inherited
▶ public Felidae(bool male)
▶ {
▶ this.male = male;
▶ }
▶ public bool Male
▶ {
▶ get { return male; }
▶ set { this.male = value; }
▶ }
▶ }

▶ public class Lion : Felidae
▶ {
▶ private int weight;
▶ // Keyword "base" will be explained in the next paragraph
▶ public Lion(bool male, int weight) : base(male)
▶ {
▶ this.weight = weight;
▶ }
▶ public int Weight
▶ {
▶ get { return weight; }
▶ set { this.weight = value; }
▶ }
▶ }

Access Modifiers of Class Members
and Inheritance
▶ All of its public, protected and protected internal members
(methods, properties, etc.) are visible to the inheriting class.
▶ All of its private methods, properties and member-variables are not
visible to the inheriting class.
▶ All of its internal members are visible to the inheriting class, only if the
base class and the inheriting class are in the same assembly.

Virtual Methods:
class BC
{
public virtual void Display()
{
System.Console.WriteLine("BC::Display");
}
}
class DC : BC
{
public override void Display()
{
System.Console.WriteLine("DC::Display");
}
}
class Demo
{
public static void Main()
{
BC b;
b = new BC();
b.Display();
b = new DC();
b.Display();
}
}
BC::Display
DC::Display

abstraction
▶ Abstraction means working with something we know how to use
without knowing how it works internally. A good example is a
television set.
▶ Abstraction allows us to do something very important – define an
interface for our applications, i.e. to define all tasks the program is
capable to execute and their respective input and output data.

▶ public class AbstractionExample
▶ {
▶ static void Main()
▶ {
▶ Lion lion = new Lion (true, 150);
▶ Felidae bigCat1 = lion;
▶ AfricanLion africanLion = new AfricanLion (true, 80);
▶ Felidae bigCat2 = africanLion;
▶ }
▶ }

Interfaces:
▶ In the C# language the interface is a definition of a role (a group of abstract actions).
▶ It defines what sort of behavior a certain object must exhibit, without specifying how
this behavior should be implemented.
▶ An interface can only declare methods and constants.
▶ A method is identified by its signature. The return type is not a part of it. If two
methods' only difference is the return type (as in the case when a class inherits
another), then it cannot be unequivocally decided which method must be
executed.

public interface IReproducible<T> where T : Felidae
{
T[] Reproduce(T mate);
}
public class Lion : Felidae, IReproducible<Lion>
{
Lion[] Reproducible<Lion>.Reproduce(Lion mate)
{
return new Lion[] { new Lion(true, 12), new Lion(false, 10) };
}
}

When Should We Use Abstraction and Interfaces?
The answer to this question is: always when we want to achieve
abstraction of data or actions.
Working through interfaces is common and a highly recommended
practice – one of the basic rules for writing high-quality code.
It is always a good idea to use interfaces when functionality is exposed
to another component.

ENCAPSULATION
It is also called "information hiding". An object has to provide its users only
with the essential information for manipulation, without the internal details.
Therefore parts of the properties and methods remain hidden to her.

public class Felidae
{
public virtual void Walk()
{
}
}
{
private Paw frontLeft;
private Paw frontRight;
private Paw bottomLeft;
private Paw bottomRight;
private void MovePaw(Paw paw)
{
}
public override void Walk()
{
this.MovePaw(frontLeft);
this.MovePaw(frontRight);
this.MovePaw(bottomLeft);
this.MovePaw(bottomRight);
}
}

POLYMORPHISM
Polymorphism allows treating objects of a derived class as objects of
its base class.
Polymorphism can bear strong resemblance to abstraction, but it is
mostly related to overriding methods in derived classes, in order to
change their original behavior inherited from the base class.

Abstract Classes
What happens if we want to specify that the
class Felidae is incomplete and only its successors can have
instances?
This is accomplished by putting the keyword abstract before the name
of the class and indicates that the class is not ready to be
instantiated.
Abstract classes, as well as interfaces, cannot be instantiated.

public abstract class Felidae
{
protected void Hide()
{
}
protected void Run()
{
}
public abstract bool CatchPrey(object prey);
}
{
protected void Ambush()
{
}
public override bool CatchPrey(object prey)
{
base.Hide();
this.Ambush();
base.Run();
// …
return false;
}
}

Object

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