1. Objects First with Java
Lab 4: Circle Outline
Replace this with your course title and your name/contact details.
© David J. Barnes and Michael Kölling

2. 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

3. 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;
© David J. Barnes and Michael Kölling

4. Objects First with Java
Constructors
public Square(int x, int y) {
this.x = x;
this.y = y;
size = 50;
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
© David J. Barnes and Michael Kölling

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

6. Method & Field Practice
Objects First with Java
Method & Field Practice
Modify the Circle class to display a colored outline:
Add a field outlineColor, plus get & set methods
Add another constructor that takes the outline color as a parameter
What should the outline color be set to in the original constructors?
Update paintComponent to draw the outline AND the filled oval (hint: use drawOval)
Use your Picture applet to test and make sure the outline is showing up correctly
Constructor + method practice
THEN talk about what they’re going to do next time… with making the applet interactive
© David J. Barnes and Michael Kölling

7. Extra: Change to Square & Triangle
Make similar changes to Square and Triangle that you did to Circle
Add a constructor that accepts as parameters the initial x and y positions, radius, and color
Add a field outlineColor, plus get & set methods
Add another constructor that takes the outline color as a parameter
What should the outline color be set to in the original constructors?
Update paintComponent to draw the outline AND the filled oval
Use your Picture applet to test and make sure the outline is showing up correctly

8. What we did today … Concepts practiced
Constructors
Methods
Classes
Modified the Circle, Square, and Triangle classes:
Added the ability to have a different colored outline

9. Homework
Finish lab exercise
Read Chapters 2 and 3