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

Student

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

public string getLetterGrade()

public void printTranscript(Student s)
{
System.out.println(s.getLetterGrade());
}

• 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