Terminology

• An object is a data structure whose class can be determined by the system. Objects are also called instances of a class.

• Conceptually, a class is a set of similar objects.

  The classes we will use include integer, symbol, null, pair, mobile, box, triangle.

  A class defines a set of methods that can be used on members of the class. The class of an object can be found using (class object). In DrScheme, use drclass.

• A method is a procedure that performs some operation on a member of a class. A method is specialized to the implementation of the class.

• A message is an indirect procedure call. A message is sent using the function send: In DrScheme, use drsend.

  (send object 'selector arguments)

• A selector is the generic name of a method, i.e., each class to which the message might be sent will define a method corresponding to the selector.

  A selector can be thought of as an abstract procedure name.

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