CSharp-learning/C# Full Course for free/14.OOP.md

# OOP

# classes

In another file
```C#
class Messages()
{
    public static void Hello()
    {
        Console.WriteLine("Hello! Welcome to the program");
    }
    public static void Waiting()
    {
        Console.WriteLine("I am waiting for somtething");
    }
    public static void Bye()
    {
        Console.WriteLine("Bye! Thanks for visiting");
    }
}
```

```C#
    Messages.Hello();
```

## Object

Object is an instance of a class
can have fields & nethods

```C#
class Human
{
    String name;
    int age;

    public void Eat()
    {
        Console.WriteLine(name + " is eating");
    }
    public void Sleep()
    {
        Console.WriteLine(name + " is sleeping");
    }
}
```

```C#
// in the main class
Human human1 = new Human()

human1.name = "Rick";
human1.age = 65;

human1.Eat();
human1.Sleep();

Human human2 = new Human()

human1.name = "Morty";
human1.age = 16;

human1.Eat();
human1.Sleep();
```

## Construtor

Constructor is a special method in a class

```C#
class Human
{
    String name;
    int age;

    public Human(String name, int age){
        this.name = name;
        this.age = age;
    }

    public void Eat()
    {
        Console.WriteLine(name + " is eating");
    }
    public void Sleep()
    {
        Console.WriteLine(name + " is sleeping");
    }
}

```

```C#
// in the main class

Human human1 = new Human("Rick",65)
Human human2 = new Human("Morty", 16)

human1.Eat();
human1.Sleep();
human2.Eat();
human2.Sleep();
```

## static

static is a modifier to declare a static member, which belongs to the class itself
rather than to any specific object

```C#
class Car
{
    String model;
    public static int numberOfCars;

    public Car(String model)
    {
        this.model = model;
        numberOfCars++;
    }
    public static void StartRace()
    {
        Console.WriteLine("The race as begun !")
    }
}
```

```C#
// in the main class

Car car1 = new Car("Mustang");
Car car2 = new Car("Corvette");
 Console.WriteLine(Car.numberOfCars);

Car.StartRace();
```

## overladed constructo

Technique to create multiple constructors, with a different set of parameters but the same name.
name + parameters = signature

```C#
class Pizza
{
    String bread;
    String sauce;
    String cheese;
    String topping;

    public Pizza(String bread,String sauce, String cheese, String topping)
    {
        this.bread = bread;
        this.sauce = sauce;
        this.cheese = cheese;
        this.topping = topping;
    }

    public Pizza(String bread,String sauce, String cheese)
    {
        this.bread = bread;
        this.sauce = sauce;
        this.cheese = cheese;
    }

    public Pizza(String bread,String sauce)
    {
        this.bread = bread;
        this.sauce = sauce;
    }

    public Pizza(String bread)
    {
        this.bread = bread;
    }

}
```

```C#
// Main

Pizza pizza = new Pizza("stuffed crust", "red sauce", "mozzarella");
Pizza pizza1 = new Pizza("stuffed crust", "red sauce");
```

## inheritance

1 or more child classes recieving fields, methods, etc. from a common parent

```C#
class Vehicle
{
    public int speed = 0
    
    public void go()
    {
        Console.WriteLine("this vehicle is moving !");
    }
}

Class Car : Vehicle
{
    public int wheels = 4;
}
Class Bicycle : Vehicle
{
    public int wheels = 2;
}
Class Boat : Vehicle
{
    public int wheels = 0;
}
```

```C#
// Main

Car car = new Car();
Bicycle bicycle = new Bicycle();
Boat boat = new Boat();

Console.WriteLine(car.speed());
Console.WriteLine(car.wheels());
Console.WriteLine(car.go());

Console.WriteLine(bicycle.speed());
Console.WriteLine(bicycle.wheels());
Console.WriteLine(bicycle.go());

Console.WriteLine(boat.speed());
Console.WriteLine(boat.wheels());
Console.WriteLine(boat.go());
```

## abstract classes

modifier that indicates missing components or incomplete implemetation

```C#
abstract class Vehicle
{
    public int speed = 0
    
    public void go()
    {
        Console.WriteLine("this vehicle is moving !");
    }
}

Class Car : Vehicle
{
    public int wheels = 4;
    int maxSpeed = 500; 
}
Class Bicycle : Vehicle
{
    public int wheels = 2;
    int maxSpeed = 50; 
}
Class Boat : Vehicle
{
    public int wheels = 0;
    int maxSpeed = 100; 
}
```

```C#
// Main
Car car = new Car();
Bicycle bicycle = new Bicycle();
Boat boat = new Boat();
Vehicle vehicle new Vehicle();
// error can't instanciate
```

## array of object

```C#
Class Car 
{
    public String model;
    public Car(String model)
    {
        this.model = model;
    }
}
```

```C#
// main
Car[] garage = new Car[3]

Car car1 = new Car("Mustang");
Car car2 = new Car("Corvette");
Car car3 = new Car("Lambo");

garage[0] = car1
garage[1] = car2
garage[2] = car3

// or with anonymous object

Car[] garage = {new Car("Mustang"), new Car("Corvette"), new Car("Lambo")}

forach(Car car in garage)
{
    Console.WriteLine(car.model());
}
```

## Object as arguments


```C#
Class Car 
{
    public String model;
    public String color;

    public Car(String model, String color)
    {
        this.model = model;
        this.color = color;
    }
}
```

```C#
// main

Car car1 = new car("Mustang", "red");
Car car 2 = Copy(car1)

ChangeColor(car1, "siver");

Console.WriteLine(car1.color + " " + car1.model)

Console.WriteLine(car2.color + " " + car2.model)

public static void ChangeColor(Car car, String color)
{
    car.color = color;
}

public static Car Copy(Car car)
{
    return new Car(car.model, car.color);
}
```

## method overiding

provides a new version of a method inherited from a parent class
inherited method must be: abstract, virtual, or already overriden
Used with Tostring(), polymporphism

```C#
Class Animal
{
    public virtual void Speak()
    {
        Console.WriteLine("The animal goes *brrr*")
    }
}
Class Dog : Animal
{
    public override void Speak()
    {
        Console.WriteLine("The dog goes *Woof*")
    }

}
Class Cat : Animal
{
    public override void Speak()
    {
        Console.WriteLine("The cat goes *Meow*")
    }
}
```

```C#
    Dog dog = new Dog();
    Cat cat = new Cat();

    dog.Speak();
    cat.Speak();
```

## ToString

Converts an object ot its string representation so that it is suitable for display

```C#
class Car
{
    String make;
    String model;
    int year;
    String color;

    public Car(String make,String model,int year,String color)
    {
        this make = make;
        this model = model;
        this year = year;
        this color = color;
    }
    
    public overide ToString()
    {
        String message = "this is a " + make + " " + model;
        return message;
    }
}
```

```C#
// Main

Car car = new Car("Chevy", "Corvette", 2022, "blue");

Console.WriteLine(car);
```

## Polymporphism

Objects can e identified by more than one type
Ex. A Dog is also: Canine, Animal, Organisms

```C#
class Vehicle
{
    public int speed = 0
    
    // have to add virtual for polymporphism
    public virtual void Go()
    {
        Console.WriteLine("this vehicle is moving !");
    }
}

Class Car : Vehicle
{
    public int wheels = 4;
    public overide void Go()
    {
        Console.WriteLine("this car is moving !");
    }
}
Class Bicycle : Vehicle
{
    public int wheels = 2;
    public overide void Go()
    {
        Console.WriteLine("this go is moving !");
    }
}
Class Boat : Vehicle
{
    public int wheels = 0;
    public overide void Go()
    {
        Console.WriteLine("this boat is moving !");
    }
}
```

```C#
// Main
Car car = new Car();
Bicycle bicycle = new Bicycle();
Boat boat = new Boat();

Vehicle[] vehicles = {car, bicycle, boat};

forach (vehicle vehicle in vehicle)
{
    vehicle.Go();
}
```

## interfaces

defines a "contract" that all the classes inheriting from should follow
An inerface declares "what a class should have"
An inheriting class defines "how it should do it"
Benefit are security + multiple iheritance + "plug-and-play"


```C#
interface IPrey
{
    void Flee();
}

interface IPredator
{
    void Hunt();

}

class Rabbit : IPrey
{
    pulic void Flee()
    {
        Console.WriteLine("The rabbit run away!");
    
    }

}

class hawk : IPredator
{
    pulic void Hunt()
    {
        Console.WriteLine("The hawk is searching for food!");
    }

}

class fish : IPrey, IPredator
{

    pulic void Flee()
    {
        Console.WriteLine("The fish swims away!");
    
    }
    pulic void Hunt()
    {
        Console.WriteLine("The fish is searching for food!");
    }
    

}

```
```C#
// Main

Rabbit rabbit = new Rabbit();
Hawk hawk = new Hawk();
Fish fish = new Fish();

rabit.flee();
hawk.hunt();
fish.flee();
fish.hunt();
```

## getter and setter

getter & setters add security to fields by encapsulation
They're accessors found within properties

properties = combine aspects of both fields and methods (share name with a field)
get accessor = used to return the property value
set accessor = used to assign a new value
value keyword = defines the value being assigned by the set (parameter)


```C#
Class Car
{
    private int speed;

    public Car(int speed)
    {
        Speed = speed;
    }

    // properties
    public int Speed
    {
        
        get { return speed}; //read
        set
        {
            if value(value > 500)
            {
                speed = 500;
            }else{
                speed = value;
}
        }

    }
}
```

```C#
// Main

Car car = new Car();

Car Speed = 10000000000; 

Console.WriteLine(car.Speed);
```

## Auto-Implemted properties

shortcut when no additional logic is required in the property
you do not have to define a field for a property,
you only have to write get; and/or set; insid the property;

```C#
Class Car
{
    // shortcut
    public String Model {get; set;}
    public Car(String model)
    {
        this.Model = model;
    }
}
```

## Enums

Special "class" that contains a set of named integer constans.
use enums when you have values that you know will not change,
To get the integer value from an item, you must explicitly convert to an int

name = integer

```C#
enum Planets
{
    Mecury, 
    Venus, 
    Earth, 
    Mars, 
    Jupiter, 
    Saturn, 
    Uranus, 
    Neptune, 
    Pluto
}

enum PlanetsRadius
{
    Mecury = 2439, 
    Venus = 6051, 
    Earth = 6371, 
    Mars = 3389, 
    Jupiter = 69911, 
    Saturn = 58232, 
    Uranus = 25362, 
    Neptune = 24622, 
    Pluto = 1188
}


Console.WriteLine(Planets.Pluto + " is a planet")


String name = PlanetsRadius.Earth.ToString();
// return : Earth

int radius = (int)PlanetsRadius.Earth;
// return : 6371
```

## generics

not specific to a particular data type
add <T> to : classes, methods, fields, etc.
or other name ex : <Things>
allow for code reusability for different data types

```C#
int[] intArray = { 1, 2, 3};
double[] doubleArray = { 1.0, 2.0, 3.0};
String[] stringArray = {"1","2","3"};

// don't work for other array
public static void() displayElements<T>(T[] array)
{
    foreach(T item in array)
    {
        Console.Write(item + " ")
    }

}
```