Outline of Class 8: Interfaces and More

Held: Friday, January 30, 1998

Administrivia

• Randy Smith of Torrent Systems, Inc., a "Parallel Software Infrastructure Company", will give a talk entitled The Programming They Don't Teach You In College on Monday, February 9, as part of the noon brown-bag lunch series. He'll also meet with students at 1pm in the forum for an informal lunch. Mr. Smith has worked for Thinking Machines, the Open Software Foundation, and the Free Software Foundation. Sign up with Sam Rebelsky if you'd like to meet with Mr. Smith.
• There were a number of votes to move to the other classroom, in spite of its limitations. I'll email you when/if I decide to move.
• Today's outline is sketchy because our system was down when I tried to write it.

Interfaces

• Instead of relying on multiple inheritance, Java permits you to declare interfaces, collections of routines that an object can agree to support.
• For example, we might decide to may our complex numbers, which are most likely a subclass of Number agree to provide a set of drawing routines.
• Similarly, we might decide that Line objects, which would most likely be a subclass of Polygon (or some such) would also provide "mathematical" operations (so that you could add, subtract, and compare lines).
• Interface declarations look remarkably like class declarations, except that
  • You use interface instead of class.
  • You cannot include fields in an interface.
  • You do not give bodies to your interface's methods
• A class agrees to implement all the routines in an interface by using the implements keyword, as in

  public class Complex 
    implements Drawable 
  {
    ...
  } // Complex
  

• If you implement more than one interface, separate them by commas.
• Once you've defined an interface, you can treat interfaces as classes, at least in terms of providing variables (and, I think, fields). For example, the following should be perfectly legal

  Drawable d = new Complex();