Java Execution Model and Methods

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Today's agenda:

Java Execution Model (JEM) example
Overview of Java methods
Writing Java Methods

Go to the CS111 download directory using the cs111d account on puma, and download the lab2_programs folder to your desktop.

Buggles and BuggleWorld

Exercise 1: JEM

Draw JEM for the following example:

Exercise 2: Welcome to ChecksWorld!!!

Open ChecksSimple.java in DrJava.

What picture does ChecksSimple.java produce?

Run the program to see the answer.

Click here for the answer

For all the Checkerboard tasks below, you will be creating new java files from scratch. However, the HTML files are provided for you.

Task 1 -- Drawing a pattern using Methods

Create a new file called ChecksMethod.java in DrJava. Save it in your lab2_programs folder.

ChecksMethod.java must define the class called ChecksMethod (like you create the Cs class last week in Cs.java)
Your run method should go inside the ChecksMethod class
Create a new class called CheckerBuggle that extends the Buggle class (this class definition can go below the ChecksMethod class definition)
Inside the new CheckerBuggle class, write a method which draws the same picture as the program in ChecksSimple.java does.
Important: You may NOT use the setPosition() method!
Note that the CheckerBuggle class is an extension of the Buggle class, so you can use all methods of the Buggle class. Here are some hints:
- In the class CheckerBuggle (in the ChecksMethod.java file) write the header of the method that will draw the picture (is it public or private? Is it void or does it return any value?). Think of a good name for the method. Put the opening and closing braces { and } for the body of the method. Do not yet write the code for the body.
- In the file ChecksMethod.java, create a new CheckerBuggle in the method run() and invoke the new method (the one that you are writing) on this CheckerBuggle. Compile and run the program. Since there is nothing in the body of the method yet, you should only see the new buggle on the applet, but no drawing.
- Fill in the body of the method. As you are writing the code, compile and run your program after adding every 1-2 lines. This way you can discover and correct any errors immediately.

Task 2 -- Drawing a checkerboard using Methods

Now create a new file called Checksboard.java to solve this task.

Checksboard.java requires a 5x5 grid in BuggleWorld. You need a method called init() to create the correct size grid in BuggleWorld (much like we did last week with the 13x13 grid in Cs.java). Take a look at Hi.java (included in the lab2_programs folder) as a refresher on how to use the init() method.

In the file Checksboard.java create a new instance of the class CheckerBuggle.

Then add more methods to the class CheckerBuggle and invoke some of these methods in Checksboard.java on the CheckerBuggle that you have created.

All the drawing and most of the moving must be done in methods of the class CheckerBuggle, not in run(). In this exercise and in the rest of the lab the method run() must be very short: just creating a new buggle and a few (between one and five) method invocations. If you write the program this way, it will be easier to reuse the methods from one exercise in another.

In the end of the program the buggle must be positioned as shown below. However, it may have any color (not white, as on the picture).

Task 3 -- Drawing a more complex checkerboard (using more Methods...).

Create a new file called BigChecksboard.java, with a 15x15 grid in BuggleWorld and a CheckerBuggle class.

Write BigChecksboard.java to solve the problem:

Task 4 -- And even bigger and fancier checkerboard (using more Methods...).

Create a new file called SuperBigChecksboard.java, with a 45x45 grid in BuggleWorld and a CheckerBuggle class. SuperBigChecksboard.java should create this picture:

Task 5

Create a new file called FlippedSuperBigChecksboard.java with a 45x45 grid to solve this problem: