Question

If we had a class, say MyClass, when instantiating an object of that class, what is the difference between these two:

Object obj=new MyClass();
MyClass obj2=new MyClass();

I know that in .NET, all classes derive from System.Object, so that in this case, obj and obj2 variables just contain references to the objects.

However, is there any difference?

And if so, what is it, when using these two ways of instantiating objects?

Answer 1

Supposing your class had a property called Name, if you used this,

Object obj = new MyClass();

and tried to use:

obj.Name = "George";

This would be a compiler error, because the Object class does not have a Name property. This, however, would be fine:

MyClass obj2 = new MyClass();
obj2.Name = "George";

because the obj2 is a MyClass. In short, in order to access a variable’s class members (properties, methods, variables), that variable has to be of a type that has those members, or it needs to be cast to the necessary class:

((MyClass)obj).Name = "George";

However, constantly casting variables in order to get at their members is not good, as it requires extra CPU cycles and can lead to InvalidCastExceptions.