CS 330 Lecture 28 – Inheritance and polymorphism


  • fixing our stack?
  • oop:
    • encapsulation
    • polymorphism
    • inheritance
  • is-a vs. has-a
  • inheritance tightly couples, destroys encapsulation
  • modern thinking: limit inheritance, favor shallow hierarchies and has-a composition
  • when inheritance is a good idea
    • when refactoring a library you maintain
    • when writing a GUI widget
  • polymorphism: lets you write conductor code
  • easy in dynamically-typed languages
  • in statically-typed, polymorphism achieved via:
    • overloading
    • templates
    • coding to a supertype
  • C++ favors static method binding over dynamic binding

Achievement-based Grading

How would you view this sort of grading?

Number of Programs Without final With final With participation
6 B A- A
5 C B B+
4 D C C+
3 F D D
<= 2 F F F

With these restrictions:

  • Students could choose from a broad set of programming assignments.
  • One program must be from the imperative category.
  • One program must be from the scripting language category.
  • One program must be from the functional category.
  • One program must be from the interpreters category.
  • No more than one program may be turned in each week.
  • All programs must be turned in before the last week of lecture.
  • Programs that do not meet criteria will be returned for correction.



Grades would be easy.
But you all have vtables.
You are dynamic.


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