CS 204: Software Design

Due 8:30AM Friday, 8 May 2009
You may work with a partner for this assignment.

Animation with Java and inheritance

The purpose of this project is to get you warmed up on programming in Java, and to start you thinking about program structures that make use of polymorphism and inheritance.

Run-time behavior

Your program will start with a class named Animation.java, which will have the main method that launches the program. You'll run your program via a command line like this:

java Animation sprites.txt 500 300

where sprites.txt contains a textual description of the various objects (sprites) that will be moving around in your animation, and 500 and 300 are examples of the animation window width and height, in pixels.

When you run this program, some sort of animation will take place. Spaceships in space, butterflies in a meadow, cars in a city, zombies in the park, or whatever strikes your fancy. The keys to this program will be the use of Java and adherence to the structure described in the next section, so the particulars of your animation don't matter a great deal.

I know that some of you likely did a similar project in CS 111 (or 117 if you've been around here long enough). If so, just start this one fresh, pay attention to the guidelines below, and pick a new animation context.

Program structure

Your program will consist of:

• A main method in Animation.java with a structure like this (in pseudo-code):

  Instantiate a Canvas object using the command line width and height. Open the sprites file as specified on the command line spriteList = empty ArrayList of for each line in the sprites file sprite = createSprite(line from file) sprite.setCindow(canvas) add sprite to spriteList close sprites file // Begin animation do forever for each sprite: sprite.erase() sprite.draw() pause for some fraction of a second sprite.step()

  You may want to just erase the whole canvas in your "do forever" loop. Note that I am not looking for smooth animation.

• A top-level Sprite class like this (assuming you use the Canvas library Canvas.java):

  import java.awt.*; public class Sprite { private Canvas canvas; private Point position; private Point velocity; public Sprite() { ... } /** * @param description The description line from the "sprites.txt" * input file. */ public Sprite(String description) { ... } public void step() { // Default action, if any, goes here. } public void draw() { // Probably this will just be a stub, to be overridden in the // child classes. } /* ... other methods you think the parent should have ... */ /* ... accessors for position, velocity, etc. ... */ }
• A collection of at least three subclasses of Sprite, representing the various kinds of objects you want to include in your animation. These classes will contain overrides of the methods in Sprite to arrange for the drawing, stepping, etc.

• A factory method

  public static Sprite createSprite(String description)

  in Animation.java that returns a reference to a newly instantiated object of whatever subclass of Sprite is indicated in the description string. We'll talk more about this in class.

Sprite file format

The sprite file will consist of lines of text, one per sprite, of this format:

For example:

would, presumably, cause the instantiation of an object of type Goat with initial position (200, 100) and initial velocity (10, 0) and initial color purple.

You are free to add features to your particular sprite types, making corresponding additions to the "other info" section of the sprite description line in the sprites file.

Questions? Let me know.

Have fun.