Assignment 6: Abstract Classes and Interfaces Practice

Objective: To get experience using abstract classes and interfaces.

Due: Before class on Friday.

Using Abstract Classes in the Game application (30)

To start, you can either:

• Copy your Game code from Assignment 4 into a new assign6 directory OR
• Start a new Java project in Eclipse, and on the second screen say that you're using existing source code ("Link additional source: use this if you have a folder in the file system that should be used as additional source folder") and give the path to your Assignment 4 code (the game)
  If you don't see your images when you run your code through Eclipse, it's probably because Eclipse can't find your image files. You may need to add bin/ before the location of your image files
  OR
• Start with my base code in /home/courses/cs209/handouts/assign6. To edit the code in Eclipse, you'll need to copy the files somewhere under your home directory.

Now for the refactoring of your code:

• First, clean up your code. If you did not use the @Override annotation on the move methods of your child classes, you should add that. If you get errors, fix the errors (most likely caused by not using the appropriate parameters).
• Modify the GamePiece class so that it is an abstract class with an abstract move method.
• Modify the Game class's animate method to have an array of GamePiece objects, which contains the GamePiece objects that you just created. Iterate through the objects, calling the move method on each object. (If you're getting errors, you likely didn't override the move method correctly.) You can look at my base code in /home/courses/cs209/handouts/assign6/Game.java to help guide you.

• Test your new code.
• In comments in GamePiece, discuss why making GamePiece abstract is a better approach to organizing/designing the code
• In comments in Game,
  1. explain why we can call the move method on a GamePiece object--a method that is abstract--and the application does the "right" thing
  2. discuss all the steps you would need to take to add a new Goblin that has a different movement behavior (e.g., zig-zags across the screen) to the game. Don't talk about the zig-zag behavior in particular--I just want to give you a concrete idea of a different behavior.

Using Interfaces (35)

Modify your Assignment 5 MediaItem class to implement the Comparable interface. It is up to you how you compare the items, although it should be something that makes sense.

Let Eclipse do most of the work for you. (Note that this would be a little more straightforward if you added that the class should implement an interface during creation of the class.) When you start typing to implement the Comparable interface, use control-spacebar to let Eclipse complete "Comparable", which will automatically add the parameter. Eclipse will give you an error about unimplemented methods; click on the error and select to implement methods. That will give you the method template--you still need to fill in the method.

In your driver program, sort and display the elements in the array.

Save your output in a file.

Turnin

Copy your project into an assign6 directory in your turnin directory.

Grading (65 pts)

You will be evaluated based on the following criteria:

• (30 pts) GamePiece class - abstract; testing; style; discussion comments (15)
• (35 pts) Media classes implement Comparable interface, testing; style