CMSC 433 – Programming Language
Technologies and Paradigms
Spring 2007
Abstraction
Feb. 27, 2007
Data Abstraction
• Data abstraction = objects + operations
– List + { addFirst, addLast, removeFirst, ... }
– Set + { add, contains, ...}
• Categories of operations
– Constructors (creators/producers)
– Mutators/Modifiers
–Observers
Abstraction Function
• Specification for data structure is abstract
• Implementation of data structure is concrete
• How do you know if implementation meets the
spec?
• Abstraction function : concrete abstract
– Specifies how the representation of an abstract data
type is interpreted as an abstract value.
Example
class IntSet { int[] elts; ... }
– AF(s) = { s.elts[i] | 0 <= i <= elts.length }
• You always need an abstraction function when
you build a data abstraction
– Often it’s implicit
