Lecture 8: Objects and Classes, cont

1
Lecture 8 Objects and Classes, contd

• discuss hw2
• assign h3
• Review the main points of objects/classes
• This
• Pass-by-value
• A new example our Date class

2
HW2

• Key point main program constructs an array of
  Number objects
• Then the main program processes the array,
  typically several times, printing out all the
  numbers in bases of the users choice
• There is no array inside the Number class
• If you were confused on this point you can
  resubmit for a better grade

3
HW3

• Placing queens on a chessboard

4
Classes serve 2 purposes

• A way of organizing static methods, e.g. the Math
  class
• Factories for constructing objects, which can
  then be processed by calling instance methods

5
This

• a way of referring to data fields (instance
  variables) of the object (can be omitted unless
  there is an ambiguity)
• a way of calling a constructor from another
  constructor with a different signature (the only
  way to do this?)
• a way of calling an instance method from another
  instance method (the only way to do this?)
• Only the first 2 of these are mentioned on p.236
• Example the Player class again

6
Java is a Pass-By-Value Language

• When a method is called, the values of the actual
  parameters are passed from the calling method to
  the called method
• It is not possible for the called method to pass
  changes to the actual parameters back to the
  calling method
• This applies whether the actual parameter is a
  primitive type or an object reference
• HOWEVER, if the actual parameter is an object
  reference, the called method CAN and often DOES
  change fields in the object that the reference
  points to