Classes

• A superclass (a type model which it extends or modifies)
• A set of _class_variables_, a set of _instance_variables_, and a set of _methods_.
  • Class variables are variables declared as static in the class definition.
• Objects are instances of classes.
• Information may be passed inside an object by function calls, but are passed between objects by _messages_. The _receiver_object_ is the one which controls the subsequent execution.