downcast and upcast

user_184805 0
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I am new to C# (and OOP). When I have some code like the following:

class Employee
{
    // some code
}


class Manager : Employee
{
    //some code
}

Question 1: If I have other code that does this:

   Manager mgr = new Manager();
   Employee emp = (Employee)mgr;

Here Employee is a Manager, but when I cast it like that to an Employee it means I am upcasting it?

Question 2:

When I have several Employee class objects and some but not all of them are Manager's, how can I downcast them where possible?

upcasting downcast oop c#
6 Answers

Answer 1 : Yes it called upcasting but the way you do it is not modern way. Upcasting can be performed implicitly you don't need any conversion. So just writing Employee emp = mgr; is enough for upcasting.

Answer 2 : If you create object of Manager class we can say that manager is an employee. Because class Manager : Employee depicts Is-A relationship between Employee Class and Manager Class. So we can say that every manager is an employee.

But if we create object of Employee class we can not say that this employee is manager because class Employee is a class which is not inheriting any other class. So you can not directly downcast that Employee Class object to Manager Class object.

So answer is, if you want to downcast from Employee Class object to Manager Class object, first you must have object of Manager Class first then you can upcast it and then you can downcast it.

user_94236690

Upcasting and Downcasting:

Upcasting: Casting from Derived-Class to Base Class Downcasting: Casting from Base Class to Derived Class

Let's understand the same as an example:

Consider two classes Shape as My parent class and Circle as a Derived class, defined as follows:

class Shape
{
    public int Width { get; set; }
    public int Height { get; set; }
}

class Circle : Shape
{
    public int Radius { get; set; }
    public bool FillColor { get; set; }
}

Upcasting:

Shape s = new Shape();

Circle c= s;

Both c and s are referencing to the same memory location, but both of them have different views i.e using "c" reference you can access all the properties of the base class and derived class as well but using "s" reference you can access properties of the only parent class.

A practical example of upcasting is Stream class which is baseclass of all types of stream reader of .net framework:

StreamReader reader = new StreamReader(new FileStreamReader());

here, FileStreamReader() is upcasted to streadm reder.

Downcasting:

Shape s = new Circle(); here as explained above, view of s is the only parent, in order to make it for both parent and a child we need to downcast it

var c = (Circle) s;

The practical example of Downcasting is button class of WPF.

user_82686870
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