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Material Type: Notes; Class: LAB:Comp Program & Prob Solv; Subject: Computer Science; University: Wellesley College; Term: Fall 2007;
Typology: Study notes
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Department of Computer Science Wellesley College
Friday, Sep. 7, 2007
OOP 2-
I don’t think that word means what you think it means
argument
parameter
class
variable
object
double
static
method float
instance
OOP 2-
becky in BuggleWorld
becky the Buggle
BuggleWorld
OOP 2-
Four properties of Buggles
o position: Where becky sits, specified by an (x, y) coordinate. o heading: The compass direction becky is facing. o color: becky and her paint brush’s color. o brushDown: Is becky ready to paint?
*Collectively these four properties define the state of a Buggle.
OOP 2-
A class is described by
instance variables that describe the properties of each class instance; and
instance methods that are the messages to which an instance of the class can respond.
becky
betty
bernice
OOP 2-
Methods with arguments (aren’t we sassy?)
o Some methods require additional information when they are invoked. o The additional information passed to the method is called an
becky.setColor(Color.yellow); becky.forward(3);
OOP 2-
Contracts
OOP 2-
Creating New Buggles
becky
betty
bernice
Buggle becky = new Buggle(); becky.brushUp(); becky.forward(7);
Buggle bernice = new Buggle(); bernice.setColor(Color.magenta); bernice.forward(5);
Buggle betty = new Buggle(); betty.setColor(Color.blue);
OOP 2-
An Example of a Class and Method public class BreakfastWorld extends BuggleWorld { public void run () { Buggle becky = new Buggle(); // becky goes outside becky.forward(2); becky.left(); becky.forward(); becky.right(); becky.forward(); becky.right(); becky.forward(); becky.left(); // walks to the bagel becky.forward(2); // and chows down becky.pickUpBagel(); } // run()
... } // class BreakfastWorld
constructing a new Buggle object
comments
r u n m e t h o d
OOP 2-
Creating becky the Buggle
assignment statement
(^1) variable declaration 2 constructor method invocation
OOP 2-
Behind the curtain
new invokes constructor method
Variable Declaration
becky (^) assignment connects the two
position
heading
color
brushDown true
Location
Buggle
x
y
1
1
Direction
Color
OOP 2-
Are there classes other than Buggles?
o Yep!
o Java has many pre- defined classes
o And we will create many classes of our own throughout the semester
OOP 2-
Objects inside of objects
position
heading
color
brushDown true
Location
Buggle
x
y
1
1
Direction
Color
*What about contents of variablebrushDown inside of a Buggle object? Is this an object too?
OOP 2-
A notational convenience
position
heading
color
brushDown true
Buggle
EAST
red
(1,1)
OOP 2-
Expressions and Statements
becky Color.yellow 3 new Buggle() apparateLocation new Location(4,5)
becky.left(); becky.setColor(Color.yellow); Buggle bernice = new Buggle(); bernice.forward(5); Location apparateLocation = new Location(4,5); harry.setPosition(apparateLocation);
OOP 2-
Object-oriented Terminology
o Object-oriented means we create and manipulate program objects , which often represent things in the world (my car, you, becky the buggle).
o Objects are things that have state and can respond to messages. When an object receives a message, it executes the corresponding method ⎯ a named sequence of instructions that describes some behavior of an object.
o A class is a description of the shared characteristics of a group of objects. A class defines the properties ( instance variables ) that make up the state of each instance and the methods the objects understand. E.g., a buggle’s color or forward().
o An object created based on the class description is an instance of the class.
o A constructor method creates a new instance of a class.
