The document provides instructions for completing a Java lab assignment involving classes for drawing shapes and colors. It describes the required classes - ColorHolder, ColorButton, CircleButton, SquareButton, and SimpleDraw - and their relationships. ColorHolder stores and sets the current color. ColorButton defines a buttonPressed method. CircleButton and SquareButton add shapes to the Window when pressed and reference the single Window object. SimpleDraw initializes instances of these classes and adds them to the Window.

1. Victoria Minorczyk
vaminorc@buffalo.edu
Office Hours:
Thursdays 1-1:50pm
in Davis 302

2. Objects Classes
 Objects do NOT exist
until runtime.
 Run time is when your
code is actually being
executed!
 Objects are
INSTANCES of classes.
 A class is a type.
 It defines the type of
object that is
instanced (created)
from it.
 It describes (defines)
all of the properties &
behaviors that an
instance of that class
(object of that type)
will have

3. A class is like a blueprint for a Ford car. The blueprint details
exactly how that car is to be built. (How to build it, size, shape,
color, engine, ect.)
Construction
Of
Car
This is where you would
write code in Java.
Specifically, you are
defining a class! Just like
you have defined the
EcoOne and EcoTwo
classes!
You finished
defining your
classes. Now
it‟s runtime!
Your code is
compiled
(executed).
The product is an
actual object of
that class (stored
in memory). Aka
instantiation of a
class! Objects exist
only during run
time.

4. In short, a variable holds reference to an object.
-A reference is the
starting address in
memory of an object.
-Again, it is not the
object itself.
-It just tells you where
the object is in
memoery.
Victoria‟s House
Vicki‟s House
My Home
-Variables are used
to hold references.
-They are not the
objects themselves.
*Variables CAN
change their
reference
*Variable CAN hold a
„null‟ reference
1234 ApplePie Road,
Fruitsville, FL 13926
-An object is a
an instance of a
class.
-It is stored in
memory!

5. animal.Dog fido = new animal.Dog();
The variable is fido! It holds a reference to the object you just created!

6. ken = new places.Kennel();
Variable
Assignment operator
Expression (something
that can be evaluated)
Terminator
animal.Dog clifford = ken.getDog();
places.Kennel ken;
This is another example of an assignment statement with a method call as
the expression instead of a new expression:

8. animal.Dog d;
d = new animal.Dog();
Declarations
reserve space
in memory for
your variables
available
used
(reserved for d)
available
available
available
available
available
available
1000
1001
1001
1002
1003
1004
1005
1006
Then the new expression is evaluated.
It‟s value is the starting address in
memory of the newly created
animal.Dog object.

9. animal.Dog d;
d = new animal.Dog();
available
used
(reserved for d)
available
available
available
animal.Dog object
animal.Dog object
animal.Dog object
1000
1001
1001
1002
1003
1004
1005
1006
Declarations
reserve space
in memory for
your variables
Then the new expression is evaluated.
It‟s value is the starting address in
memory of the newly created
animal.Dog object.
Finally, the assignment
operator stores value of
the express in the spot in
memory reserved for d

10. animal.Dog d;
d = new animal.Dog();
Declarations
reserve space
in memory for
your variables
available
1004
available
available
available
animal.Dog object
animal.Dog object
animal.Dog object
1000
1001
1001
1002
1003
1004
1005
1006
Then the new expression is evaluated.
It‟s value is the starting address in
memory of the newly created
animal.Dog object.
Finally, the assignment
operator stores value of
the express in the spot in
memory reserved for d

11.  These are variables that belong to the class
and not to the object(instance)
 They are initialized only once, at the start
of the execution.
 They are initialized first. (before
initialization of instance and local variables)
 A single copy is shared by all instances of the
class
 A static variable can be accessed directly by
class name
 Syntax : <class-name>.<variable-name>

12. public class Leaf {
private java.awt.Color _color;
public Leaf(java.awt.Color c){
_color = c;
}
}
public class Tree {
private Leaf _l1;
private Leaf _l2;
public Tree(){
_l1 = new Leaf(java.awt.Color.GREEN);
}
}

13. t

14. public class Tree {
private Leaf _l1;
private Leaf _l2;
public Tree(){
_l1 = new Leaf();
_l1.setColor(java.awt.Color.GREEN);
}
public getLeaf(){
return _l1;
}
public addLeaf(Leaf incomingLeafObject){
_l2 = incomingLeafObject;
}

15. Tree
o Tree( )
o getLeaf( )
o addLeaf(Leaf)
Method headers
with parameter
types ONLY not
variable names
class name
Constructor header
with parameters
listed

16. public class Leaf {
private java.awt.Color _color;
public Leaf(java.awt.Color c){
_color = c;
}
}

17. Leaf
o Leaf(java.awt.Color)

18. Leaf
o Leaf(java.awt.Color)
Tree
o Tree( )
o getLeaf( )
o addLeaf(Leaf)
What relationship does this arrow represent?
What other relationships have we learned so far?

20.  Keep calm. You have two
weeks to finish this lab,
however…
 Don’t be lulled into a
false sense of security.
This lab is a lot of work. Do a
little part of it each day.
 Remember: You can do
this! You have all the
resources you need to
complete this lab. Check your
lecture notes if you get stuck
or attend office hours.

21.  It‟s a really good
idea to actually
read the lab
description.
 It tells you (in
natural language)
exactly how to
solve the lab step-
by-step.
 Just convert it to
Java!

22. • You only need to complete the ones in
the lab4 package!
• This means define the SquareButton, SimpleDraw, ColorButton,
CircleButton and ColorHolder classes.
• If you change stuff in classes besides these…there could be problems

• The UML diagram are given for the classes you need to define. You
should be very happy about this. Remember what UML diagrams
contain? 

23.  Holds the “current color”
 Defines two methods: „getColor‟ and
„setColor‟
 Has a single instance variable of type
jave.awt.Color
 It‟s constructor initializes instance variable
to java.awt.Color.WHITE
 IMPORTANT: For the system to work properly
there must be exactly(one ColorHolder
instance in your finished system.)

24.  The colorButton class defines a
“buttonPressed” method.
 The “buttonPressed” method is called when
the mouse is clicked over the top of a
ColorButton

25.  Defines a “buttonPressed” method
 When the circle button is pressed, a new
supportcode.Square must be added to the
supportcode.Window.
 You can do this by using the Window‟s
addCircle method.
 NOTE: there is only ONE instance of the
supportcode.Window class. The squareButton
classes keeps a reference to it!
 IMPORTANT: the parameters for the
constructor of this class must be declared in
the order given in the UML diagram.

26.  Refer to “squareButton class” slide.
 Replace all the words “square” with “circle”

27.  Its constructor creates an instance of the
Window class, the ColorHolder class,
CircleButton class, SquareButton class and
three instances of the ColorButton classes.
 Constructor also adds the SquareButton and
CircleButton to the Window; call the Window
object‟s addSquareButton and
addCircleButton method to do this.
 Constructor also adds the ColorButton
objects to the Window by calling the
Window‟s addColorButton method