CMSC 10200

1
Programming the WWW II

• CMSC 10200
• Spring 2003
• Lecture 3

2
More about methods and classes

• Exam information
• Debugging information
• Overloading
• Decomposition
• Relationships -- association aggregation
• Applets and graphics

3
Debugging information

• Different kinds of errors (run-time,
  compile-time, logic errors)
• When debugging applets, appletviewer can give you
  run-time error messages that are difficult to get
  from a browser

4
Exam

• Thursday
• Read texts, notes, quizzes
• Questions, find errors in code, write small bits
  of code, evaluate/interpret code

5
Method overloading

• A class may have multiple methods of the same
  name but different parameter lists
• The parameters may differ in number and/or type
• Similar operations on different types
• The return types may also vary

6
Overloading in Java

• Java uses overloading in its standard libraries
• Ex. System.out.println, Math.abs
• You may create your own overloaded methods
• Ex overloaded constructors, overloaded math ops

7
Decomposition

• Procedural decomposition is the process of
  breaking a complicated task down into smaller
  pieces.
• In Java, one complicated method may be rewritten
  as a simple method that invokes other methods to
  handle the pieces
• Example Bank account withdrawal

8
Object relationships

• Association/use (is aware of)
• Aggregation (has a)
• Inheritance (is a) (more on this later)

9
Association

• Weve seen this -- PairOfDice is aware of Die,
  etc.
• We can also have relation between instances of
  the same class
• String methods (concat,equals,etc)

10
Rational Number class

• Aggregation encapsulation of data
• Associates objects of same class
• How do we handle divide by zero? Doing this in a
  nice way is a big question in computer
  science!!!
• We can aggregate objects as well as primitive data