Question

I have a collection of classes that inherit from an abstract class I created. I’d like to use the abstract class as a factory for creating instances of concrete implementations of my abstract class.

Is there any way to hide a constructor from all code except a parent class.

I’d like to do this basically

public abstract class AbstractClass {     public static AbstractClass MakeAbstractClass(string args)     {         if (args == 'a')             return new ConcreteClassA();         if (args == 'b')             return new ConcreteClassB();     } }  public class ConcreteClassA : AbstractClass { }  public class ConcreteClassB : AbstractClass { } 

But I want to prevent anyone from directly instantiating the 2 concrete classes. I want to ensure that only the MakeAbstractClass() method can instantiate the base classes. Is there any way to do this?

UPDATE
I don’t need to access any specific methods of ConcreteClassA or B from outside of the Abstract class. I only need the public methods my Abstract class provides. I don’t really need to prevent the Concrete classes from being instantiated, I’m just trying to avoid it since they provide no new public interfaces, just different implementations of some very specific things internal to the abstract class.

To me, the simplest solution is to make child classes as samjudson mentioned. I’d like to avoid this however since it would make my abstract class’ file a lot bigger than I’d like it to be. I’d rather keep classes split out over a few files for organization.

I guess there’s no easy solution to this…

Answer 1

You can make the sub classes child classes, something like this:

public abstract class AbstractClass {     public static AbstractClass MakeAbstractClass(string args)     {         if (args == 'a')             return new ConcreteClassA();         if (args == 'b')             return new ConcreteClassB();     }      private class ConcreteClassA : AbstractClass     {     }      private class ConcreteClassB : AbstractClass     {     } } 

@Vaibhav This does indeed mean that the classes are also hidden. But this is as far as I am aware the only way to completely hide the constructor.

Edit: As others have mentioned the same thing can be accomplished using Reflection, which might actually be closer to what you would like to be the case – for example the above method replies on the concrete classes being inside the same file as the Abstract class, which probably isn’t very convenient. Having said that this way is a nice ‘Hack’, and good if the number and complexity of the concrete classes is low.