SUmmary of Class Presentation for June 24, 1999
	Topics:  Interfaces

	Java provides a feature that supports the advantages of 
multiple inheritance without most of the disadvantages.  This feature is 
the interface.  An interface is defined by:
	interface name {
		constants
		variables
		method headers
		}
All the declared variables are automatically final and static.  All the 
methods are automatically public.  There is no code in an interface.
	Classes can implement an interface by 
		class sample implements interfacea { ... }
Implementing an interface provides a class with all the constants and 
variables defined within that interface and obligates the class to 
implement all the methods whose headers appear in the interface.
	Classes may implement more than one interface:
		class sample implements interfacea, interfaceb, interfacec		 {      }   
	Interfaces specify types as do classes.  On the previous line, 
sample specifies a sample type and objects of class sample are members of
that type.  Objects of class sample are also members of the interfacea,
interfaceb, and interfacec types.  As many classes as you wish may 
implement an interface and all of their objects would be members of that
interface type.

	In nearly all cases, you can think of a class as having an 
associated type.  There are two differences between classes and types:
1.  Interfaces also have associated types
2.  Even though objects of a derived class are members of the type 
associated with their base class, the dervied class objects do not get
access to private fields within the base class while all the objects of
the base class do.

	You may declare interface variables, but there are no interface 
objects.  Instead, you may assign an object of any class that implements
the interface to any interface variable or anywhere an interface value is
required ( such as when the return type of a method is declared to be an
interface or when a parameter is declared to be of an interface type).
	Interfaces can inherit from one other interface.  Classes can 
implement some or all of the methods of an interface through inheritance
from a base class.
	
	We also looked at an example of how the capabilities of an 
enumerated type in C or C++ can be provided in Java.  Basically, one
sets up a class with a private constructor that initializes a set of 
object variables of the class to have data fields with values you want to
be in the enumeration.  Then you place those values into a public array
of class object variables.