Wednesday, February 21, 2007

Lecture 16

  • polymorphism is a very powerful tool because many related classes can be handled the same way and through the same public interface.
  • java figures out which overridden method is the public interface to use

  • Undergrad
  • Graduate
  • all 'students' have a routine for calculating letter grades

public string getLetterGrade()

public void printTranscript(Student s)

  • u - undergraduate
  • g - graduate student
  • q - special student
    • these are all classes which have getLetterGrade overrides
      • print transcript(u)
      • print transcript(g)
      • print transcript(q)
Polymorphism and Arrays

  • consider an array of students
    • conglomeration of undergraduate students, graduate students and others.
  • how do we create the array?
Arrays vs. non-arrays
Student[] s; Student S;
s = new Student[5]; S= new Student(); // not legal

Graphical User Interfaces (GUI)

  • so for our programs we have started on the first line, gone through every line in sequence, and terminated at the end
  • windows does not work that way
  • the programmer doesn't determine the order of events
  • the program 'listens' for user-generated events and passes them to the event handler
  • A GUI program consists largely of event handlers that respond to events
  • you would almost never call event handler methods instead java calls them when the even happens

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