Introduction on Class

The simplest form of a class:

class Vehicle

{

}

But do not be misled by its simplicity.  With this form, we could already instantiate an object:

Behind the scene, a default constructor is provided automatically for us if we do not defined one. 

A constructor is a method with the same name as the Class. Eg Vehicle() for Vehicle Class.

As we could have many constructors, the one without any parameters – is called the default constructor.

When do we need to define the constructors and not depend on the auto generated default constructor? 

Ans: When we need to do something such as providing initial values to data (initialization of data).

The following codes define a Vehicle Class and also a main() (in Program class) to test the class:

// A class with a public variable, default constructor and overload constructor
class Vehicle
{
    public string colour;
    // Default constructor to set colour
    public Vehicle()
    {
        colour = "Gray";
    }
    // Another constructor to take in a parameter
    // Overloading - same method name but different parameters
    public Vehicle(string col)
    {
        colour = col;
    }
    // Destructor called by Garbage Collection (GC)
    //  not required most of the time as GC can do better object release than us
    ~Vehicle()
    {
    }

}

class Program
{
    static void Main(string[])
    {   
        Vehicle car = new Vehicle();
        Vehicle car2 = new Vehicle("Red");
        Console.WriteLine(car.colour);
        Console.WriteLine(car2.colour);
        Console.ReadKey();
    }
}