1. Object Oriented Design: Identifying Objects

2. Objects First with Java
Review
What did we do in the last lab?
What did you learn?
What classes did we use?
What objects did we use?
What is the difference between a
class and an object?
What
© David J. Barnes and Michael Kölling

3. Classes An object is defined by a class
A class is the blueprint of an object:
A class represents a concept, and an object represents the embodiment (i.e., concrete instance) of that concept
The class uses methods to define behaviors of the object
Multiple objects can be created from the same class
Copyright © 2012 Pearson Education, Inc.

4. Class = Blueprint
One blueprint to create several similar, but different, houses:
Copyright © 2012 Pearson Education, Inc.

5. Let’s play a game: Identify
Objects First with Java
Let’s play a game: Identify
Classes
Behaviors/actions
Information/data
Input/output
Break out into groups for angry birds
Use the Word document handout for them to fill in classes, data, and behaviors
Go and Play the Wii ~15 minutes
© David J. Barnes and Michael Kölling

6. Objects First with Java
Basic class structure
public class ClassName {
Fields
Constructors
Methods }
Three major components of a class:
Fields – store data for the object to use
Constructors – allow the object to be set up properly when first created
Methods – implement the behavior of the object
© David J. Barnes and Michael Kölling

7. Classes/objects (state/behaviors)
Car
My first car – a maroon Saab 9000
Chair
Book
Java Software Solutions, 7th Edition
Java Software Solutions, 8th Edition
Table
Student
Teacher

8. Objects First with Java
More Identification
Think about activities you do everyday
What real-world entities do you interact with?
What about programs you use?
Your phone, laptop/desktop
Identify
Classes
Information/data
Behaviors/actions
Use the Word document handout for them to fill in classes, data, and behaviors
Identify (~4+ minutes)
Share/Group (3-4 people; ~6+ minutes)
Choose one from the group that everyone is pretty familiar with and write as much detail as you can on the board (~4 minutes)
Share/Class (~4+ minutes)
© David J. Barnes and Michael Kölling

9. Objects First with Java
Basic class structure
public class ClassName {
Fields
Constructors
Methods }
Three major components of a class:
Fields – store data for the object to use
Constructors – allow the object to be set up properly when first created
Methods – implement the behavior of the object
© David J. Barnes and Michael Kölling

10. Object-Oriented Programming (OOP)
Objects First with Java
Object-Oriented Programming (OOP)
Objects make it easier to reuse code that others have written
Java comes with built-in OO functionality (standard library)
Objects commonly represent real-world entities
For instance, an object might be a particular employee in a company
Each employee object handles the processing and data management related to that employee
OO is to programming like the assembly line was to industrialization
Explain again, WHY we care about Object-Oriented Programming
Purpose – make it easy to reuse code
OO is to programming like the assembly line is to industrialization
Copyright © 2012 Pearson Education, Inc.
© David J. Barnes and Michael Kölling

11. Objects First with Java
Fields
Fields store values for an object.
They are also known as instance variables.
Fields define the state of an object.
public class Square {
private int x;
private int y;
private int size;
private Color fillColor;
// Further details omitted. }
type
visibility modifier
variable name
private int size;
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling
© David J. Barnes and Michael Kölling

12. Similar Names for Fields
All of these terms can be used interchangeably:
Fields
Instance Variables
Characteristics
Data
Attributes
Properties
The values of the fields define the object’s _______
state

13. Data Types boolean char int long float double String Student
(any class)
— true, false
— a…z,A…Z,[symbols]
— integers
— larger integers (2x)
— floating decimal
— larger floating decimal (2x)
— characters strung together
— defined class

14. 8 Primitive Data Types in Java
Four represent integers:
byte, short, int, long
Two represent floating point numbers (with decimals):
float, double
One represents single characters:
char
One represents boolean values:
boolean
What about other data?
It must be defined as a class!
Copyright © 2012 Pearson Education, Inc.

15. Numeric Primitive Data
Why so many types to hold numbers?
Different sizes affect what values can be stored:
Type
byte
short
int
long
float
double
Storage
8 bits
16 bits
32 bits
64 bits
Min Value
-128
-32,768
-2,147,483,648
< -9 x 1018
+/- 3.4 x 1038 with 7 significant digits
+/- 1.7 x with 15 significant digits
Max Value
127
32,767
2,147,483,647
> 9 x 1018
Copyright © 2012 Pearson Education, Inc.

16. Objects First with Java
Constructors
public Square() {
x = 0;
y = 0;
size = 0;
fillColor = Color.blue; }
Constructors initialize an object.
They have the same name as their class.
They store initial values into the fields.
They often receive external parameter values for this.
Only here as a brief introduction and to reinforce what they saw last class
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling
© David J. Barnes and Michael Kölling

17. Objects First with Java
Methods
method header/signature
return type
visibility modifier
method name
/**
* Gets the size of the square. */
parameter list (empty)
public int getSize() {
return size; }
return statement
Only here as a brief introduction
start and end of method body (block)
Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling
© David J. Barnes and Michael Kölling

18. What we discussed today …
Classes and objects
What they are
How to identify them
How to identify their components
Data types

19. Homework Work on Lab 2 and submit Lab 1 Work with Codingbat exercises
Read Chapter 2