Exam 3

Question 1

encapsulation

Answer 1

group data and operations in one place

hide irrelevant deails (using visibility modifiers)

Question 2

Subtyping

Answer 2

define functions for that type

Question 3

static dispatch

Answer 3

dispatch to the parent class
easier to implement and more efficient
compiler can always tell which implementation at compile time

Question 4

dynamic dispatch

Answer 4

dispatch to the implementation based on the actual object

less efficient but provides better extensibility

Question 5

virtual table

Answer 5

shared table containing method binaries,

one per class

Question 6

Upcasting is always safe

Answer 6

Down casting not safe

Question 7

Operation classifications

Answer 7

creators, producers, mutators, observers

Question 8

Contract

Answer 8

precondition - assumptions on inputs
side effects - changes to the value
post condition - functionality of the operation
invariants - a property that is always true throughout the operation

Question 9

Why contract

Answer 9

separation of concerns:
preconditions/input values - user’s responsibility
side effects - users should be awawar of
postconditions/output values - ADT’s responsibility

Question 10

Loop invariant

Answer 10

Initially true: 
P-> Inv
true after each iter:
Inv ^E -> wp (s, Iv)
termination of loop -> post cond
Inv ^notE ->Q