1. DEFINING AND CREATING USER-
DEFINED CLASS
Chapter 6.4:

2. Writing Classes
 The programs we’ve written in previous examples
have used classes defined in the Java standard
class library
 Now we will begin to design programs that rely on
classes that we write ourselves
 True object-oriented programming is based on
defining classes that represent objects with well-
defined characteristics and functionality

3. Graphical Representation of a Class
The notation we used here is based on the industry standard notation
called UML, which stands for Unified Modeling Language.
A UML Class Diagram
Class Name
Variables
Method
Type of data
Access
Type of
return
value
A class can
contain data
declarations and
method
declarations

4. Object Instantiation
class
object

5. Object Design Questions
 What role will the object perform?
 What data or information will it need?
 Look for nouns.
 Which actions will it take?
 Look for verbs.
 What interface will it present to other
objects?
 These are public methods.
 What information will it hide from other
objects?
 These are private.

6. Design Specification for a Rectangle
 Class Name: Rectangle
 Role: To represent a geometric rectangle
 States (Information or instance variables)
 Length: A variable to store rectangle’s length (private)
 Width: A variable to store rectangle's width
(private)
 Behaviors (public methods)
- Rectangle(): A constructor method to set a
rectangle’s length and width
- calculateArea(): A method to calculate a
rectangle’s area

7. UML Design Specification
UML Class Diagram
Class Name
What data does it need?
What behaviors
will it perform?
Public
methods
Hidden
information
Instance variables -- memory locations
used for storing the information needed.
Methods -- blocks of code used to
perform a specific task.