You can ask:
How would you code a class so that can only be one object of that class?
This is known as a 'singleton'.
What does it mean to say that a method is 'static'?
How do you invoke a static method defined in one class in another class?
What access modifier is required? If the invoking class is an extension, what modifier, other that public, can be used?
What is a 'wrapper'' class?