1. Classes and Objects
B.Ramamurthy
5/9/2019
B.Ramamurthy

2. Topics for Discussion Problem to Classes
ScoreBoard class
Designing and implementing classes
Methods
Data
Using classes in an Application
5/9/2019
B.Ramamurthy

3. Problem Statement to Classes
Underline the nouns in a problem statement.
Using the problem context and general knowledge about the problem domain decide on the important nouns.
Design and implement classes to represent the nouns.
5/9/2019
B.Ramamurthy

4. Examples
Drawing package: Design a user interface for drawing various shapes: circle, square, rectangle.
Football scores: Keep track of football score.
General purpose counter: To keep of track of count for various applications.
Library: Books, different categories of books, details of student borrower, library personnel.
5/9/2019
B.Ramamurthy

5. Designing Classes A class represents a class of objects.
A class contains the data declarations (“parts”) and methods (“behaviors” or “capabilities” ).
OO Design:
Data Declarations are answers to “What is it made of?” (It has a ____, ____, etc.)
Methods are answers to “What can it do?” (verbs in the problem)
5/9/2019
B.Ramamurthy

6. ScoreBoard class class scoreBoard { //1. data int Score;
String Name; // team name
//2. Constructors : to create objects
ScoreBoard() { }; //default constructor
ScoreBoard(String teamName){ }; // initializing constructor
5/9/2019
B.Ramamurthy

7. ScoreBoard class (contd.)
//3. Interface Methods: to perform operation
void touchDown() { };
void extraPoint() { };
void twoPointConv(){ };
void fieldGoal(){ };
void safety(){ };
//4. Utility methods : to get and set
void setName(string teamName){ };
int getScore(){ };
5/9/2019
B.Ramamurthy

8. ScoreBoard class (contd.)
//5. Predicate methods :return true/false
boolean shutDown() { }; }
Implement the contents of the methods.
5/9/2019
B.Ramamurthy

9. Method Definition and Call
Specifies:
1) Name of
the function
2) The actual
parameters
Definition
Defines:
1) Header*
2) Formal parameter names
and types
3) Statements to be executed
4) Return statement(s)
5/9/2019
B.Ramamurthy

10. Method Definition : Header
body
modifiers
parameter list
return type
method name
{ statements }
5/9/2019
B.Ramamurthy

11. Parameters and Return Value
aMethod
Assume P1, P2 and P3 are integers and aMethod returns P3 which
is the sum of P1 and P2. Then definition of aMethod is:
int aMethod(int P1, int P2)
{ int P3;
P3 = P1 + P2;
return P3}
5/9/2019
B.Ramamurthy

12. Items Accessible to a Method
All the local data
All the parameters
All the data declared in the enclosing class
All the methods in the enclosing class
5/9/2019
B.Ramamurthy

13. Using Classes
An application creates objects it requires by instantiating them from classes.
The statements of the application use the accessing the public data and by invoking the public methods of the objects.
Example Application: Simulate Super Bowl (Jan 1999)
5/9/2019
B.Ramamurthy

14. Application class superBowl{ //main method …//inside main method
//1. create two object reference for the two teams
scoreBoard Denver, Atlanta;
5/9/2019
B.Ramamurthy

15. Application (contd.) // 2. instantiate objects : two ways
Denver = new scoreBoard(“Broncos”);
Atlanta = new ScoreBoard();
Atlanta.setName(“Falcons”);
//3. Use them : dot notation
Devnver.touchDown();
Denver.extraPoint();
Denver.display();
displayWinner( Denver, Atlanta);// is a method of the application }
5/9/2019
B.Ramamurthy

16. Application (contd.)
void displayWinner(scoreBoard team1, scoreBoard team2) {
System.out.println(“The winner is”);
if (team1.getScore() > team2.getScore())
team1.display();
else
team2.display(); }
5/9/2019
B.Ramamurthy

17. Creating the Executable
Enter ScoreBoard class in a file ScoreBoard.java
javac ScoreBoard.java
Enter SuperBowl application in a file SuperBowl.java
javac SuperBowl.java
Execute application by
java SuperBowl
5/9/2019
B.Ramamurthy

18. Summary We discussed complete development cycle using java classes.
Discussed (instance) methods and implementation of methods.
Using classes for instantiating objects, and dot notation for accessing items in a class were illustrated.
5/9/2019
B.Ramamurthy