Lecture 16 Objectives [Nov 20]prev next

MUSICAL COMPOSITION: Beethoven's  Ninth Symphony, 1824.
 

		This piece may take a while to get into (because of its length). But recall that Beethoven composed this symphony after he had already lost all of his hearing; he was striving for something else. While you may have heard excerpts from this symphony, it is worth one hour to hear the piece in its context.
32:05	32:05

At the end of today's class you should

HAVE READ:

• [502-508] 

KNOW:

• abstract base classes
• abstract methods

BE ABLE TO:

• Write an abstract base class for some common behavior, whose implementation is deferred to the subclasses.
• Define an abstract method

DAILY QUESTION:

• Given the example problem from Friday's class, (1) design an abstract base class that represents a Command. (2) Convert Move and Draw to be concrete derived classes from Command. (3) briefly explain the changes (if any) you need to make to Toy. [these classes are all available in SourceForge/Eclipse under nov17].

Sample Exam question(s)

1. You are responsible for designing a Toy encryption device. An encryption starts with a plain text String in capital letters (i.e., "THE PARTY WILL BE AT THE GRAVEYARD AT MIDNIGHT TELL NO ONE" and processes a sequence of Encryptions over the text. You must support the following encryptions:

• [REV] Reverse the text
• [SWAP] swap (A,Z), (B,Y), (C,X) ... (L, N) leaving M characters unchanged
• [ROTVOWELS] Rotate vowels (A -> E, E -> I, I -> O, O -> U, U -> A)
• [ROT13] Rotate13 the text (A -> N, B -> O, C -> P, ..., M -> Z, N -> A, ...)

Your encryption device must allow one to add any number of encryptions. Then, when you call method String encrypt(String plainText) an encrypted String value is returned. As a nifty trick [extra credit] try to write a String descrypt (String encryptedText) in the same class, when given an encrypted String.

2.