Admin
Midterm still being graded
•Hopefully back on Monday
Today’s topics
•Let's implement Vector!
Reading
•Ch 10 implementing class templates
Terman café today after class
Lec ture #18
ADTs (abstract data types)
Client uses class as abstraction
•Invokes public operations only
•Internal implementation not relevant!
Client can't and shouldn't muck with internals
•Class data should private
Imagine a "wall" between client and implementor
•Wall prevents either from getting involved in other's business
•Interface is the "chink" in the wall
•Conduit allows controlled access between the two
Consider Lexicon
•Abstraction is a word list, operations to verify word/prefix
•How does it store list? using array? vector? set? does it matter to
client?
Wall of abstraction
Client
Declares, init object
Doesn’t know internal
structure of object
Manipulates object through
public member functions
Lexicon lex;
lex.addWord("dog");
lex.addWord("cat");
lex.containsWord("pig");
Implementer
Knows internal structure
Has access to private data
Manipulates object in
implementing member
functions
words[nWords++] = str;
nWords
words
2
the
and
Interface
lex.nWords++;
lex.words[0] = "pig";
X
Why ADTs?
Abstraction
•Client insulated from details, works at higher-level
Encapsulation
•Internals private to ADT, not accessible by client
Independence
•Separate tasks for each side (once agreed on interface)
Flexibility
•ADT implementation can be changed without affecting client