Held: Monday, 22 September 2014

Back to Outline 13 - Exceptional Programming. On to Outline 15 - Inheritance.

Summary

We consider polymorphism, a powerful tool for code reuse (and generalization). In essence, polymorphism says that we can use different kinds of objects for the same purpose, provided they have needed charactistics.

Related Pages

• Reading: Interfaces in Java
• Reading: Polymorphism in Java
• Lab: Polymorphism
• EBoard 14 (Source 14) (HTML 14)

Overview

• Interfaces.
• Polymorphism.
• An example: Text blocks.

Administrivia

• New lab partners!
• Reminder: You can get extra credit by providing useful links.

Upcoming Work

• Daily lab writeup: http://bit.ly/207writeup
• Peer Reviews on HW4: http://bit.ly/207-2014F-peer04
• HW 5 due Tuesday.
  • Partners: AHD/TP/HZ, AS/AOA/ZW EE/CG/CMV, EF/LG/SZ/CM HB/NK/AK, WR/NS/PS, ZC/LBA/YK
• Reading for Tuesday:
  • Inheritance

Extra Credit Opportunities

Academic

• Convo next Wednesday.
• CS Table, Today: User Tracking
• Town hall meeting, 7:30 p.m. next Tuesday
• CS extras next Thursday: EF, AHD, ZW and more on MIST.

Peer Support

• Men's soccer, Saturday at some time.

Miscellaneous

• Participate in #GrinWell.
• Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too.

Interfaces

• Separate the what from the how.
• Only have signatures of methods (plus some other stuff).

Polymorphism

Warning: There is some gap between the ideal of polymorphism and its implementation in many languages, including Java.

• Use related things in the same way.
• Why should you have to write N copies of square? It should work with anything that has a multiply method.
  • And it does work that way in Scheme.
  • But Scheme trusts you. Java is your nanny.
  • (Note: Java does not provide a multipliable interface, so the theory and practice don't match as well as they should.)
• Closely tied to interfaces.
  • If you write a procedure that accepts an interface.
  • Then your procedure will work with anything that implements that interface.
• Not the same as overloading
  • Overloading requires you to write N methods for N types.
  • Polymorphism requires you to write 1 method for N types.
• Example: Text blocks.