1. February , 2009
CSE 113 B

2. Announcements 2/9: Go over Exam 1 2/11: Makeup exam for Exam 1
2/20: Exam 2 Review Sheet Available in Lecture
2/27: Lab 2 due by 11:59:59pm
3/2: Exam 2
3/4: Go over Exam 2
3/6: Exam 2 Makeup

3. Method definition syntax
public returnType nameOfMethod() { } returnType is the type of information that is returned from this method – void if nothing returned nameOfMethod is the name that the programmer picks for this method () is called a parameter list when we write the definition of a method – tells us what information is needed to complete the work of the method

4. Creating the CSE113Picture class
First, we create the file CSE113Picture.java and put inside the class definition:
public class CSE113Picture { }

5. CSE113Picture Class Functionality
We want to be able to do the following at the interactions pane:
> CSE113Picture p = new CSE113Picture();
> p.show();
And we want there to be an image shown. Therefore, we need to bring up the dialog to have the user pick an image file and then create a Picture object and then show it.

6. Constructor
In order to have the file dialog and picture created when we create a CSE113Picture, we need to use a special method that gets called whenever an object is created.
This method is called a constructor and its job is to set the initial state of the object.

7. Putting a constructor in the class definition
When we add the constructor to the class definition, we get:
public class CSE113Picture {
public CSE113Picture() { }
The constructor definition is like a method definition except:
It does not have a return type
The name of the constructor is the same as the name of the class

8. Inside the constructor
We want to put the code for getting the file dialog and creating the picture. The code inside the constructor for doing this will look basically the same as the code we wrote at the interactions pane.

9. Inside the constructor
public class CSE113Picture {
public CSE113Picture() {
Picture p = new
Picture(FileChooser.pickAFile()); }

10. Run that definition
Now, when we create a CSE113Picture, we get the file dialog and a picture gets created.
Next, all we need to do is “show” the image the user selected.
We need to write a method to show the picture.

11. Writing the show method
public class CSE113Picture { public CSE113Picture() { Picture p = new Picture(FileChooser.pickAFile()); } public void show() { p.show();

12. Problem p is not recognized outside of the constructor.
Variables declared inside a method are not accessible to other methods (even if those methods are in the same class).

13. Solution
Create a class-level variable that is accessible within the entire class.
These kinds of variables are also called instance variables.
Declaring an instance variable is the same as declaring any variable except the keyword private is placed in front.

14. Instance variable for Picture
public class CSE113Picture {
private Picture _pic;
public CSE113Picture() {
_pic = new
Picture(FileChooser.pickAFile()); }
public void show() {
_pic.show();

15. Now, when we create a CSE113Picture and call the show method on it, we can see the picture the user chooses.