PREVENTING DIRECT INSTANTIATION

We all know how objects are instantiated right? Maybe not everyone? Let's go through a quick refresher.

Objects are instantiated by using the new keyword. The new keyword allows you to create a new instance of an object, and to specify parameters to the class's constructor. You can specify no parameters, in which case the blank constructor (also known as the default constructor) is invoked. Constructors can have access modifiers, like public and private, which allow you to control which classes have access to a constructor. So to prevent direct instantiation, we create a private default constructor, so that other classes can't create a new instance.

We'll start with the class definition, for a SingletonObject class. Next, we provide a default constructor that is marked as private. No actual code needs to be written, but you're free to add some initialization code if you'd like.

public class SingletonObject
{
 private SingletonObject()
 {
  // no code req'd
 }
}

So far so good. But unless we add some further code, there'll be absolutely no way to use the class. We want to prevent direct instantiation, but we still need to allow a way to get a reference to an instance of the singleton object.