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Asteroids (Part 2)

Now that we have a functioning space ship, we'll add some asteroids to our game. To do that, we'll write an asteroid class that extends Floater. You may find slides of the Asteroids Parts 2 and 3 helpful in completing this assignment.

Suggested steps to writing an Asteroid class

  1. Create a new tab in your AsteroidsGame program. Name the new tab file Asteroid.pde.
  2. Write an Asteroid class that extends Floater in your Asteroid.pde file. You will need to write the following members and label them appropriately (public or private?):
    • a member variable to hold the speed of rotation for each asteroid
    • a constructor to initialize all 10 variables (the speed of rotation plus the 9 inherited variables from Floater)
    • a move() method that also turns (rotates) each Asteroid at its own speed
    • "getter" (accessor) functions for myCenterX and myCenterY
  3. On line 14 of index.html add Asteroid.pde to the list of files in data-processing-sources. The canvas tag should now look like <canvas id="AsteroidsGame" data-processing-sources="Asteroid.pde AsteroidsGame.pde Floater.pde Spaceship.pde Star.pde"> </canvas>. Now choose File | Save.
  4. Now add just a single asteroid to your program. Start by just calling the Asteroid's show() function. Make sure you can see it and are happy with its shape before going to the next step.
  5. Now add the code that moves and rotates the Asteroid. The best way to do this is to override the inherited move() function so that asteroids rotate as they move.

Adding an ArrayList

An array probably isn't the best way to keep track of a bunch of asteroids. Arrays have a fixed size. You can't easily add or remove asteroids from an array as they are destroyed or created. A better choice might be an ArrayList. The ArrayList class has a number of useful member methods that you are expected to how how to use on the AP exam:

  • boolean add(Object x)
  • void add(int index, Object element)
  • Object get(int index)
  • Object remove(int index)
  • Object set(int index, Object x)
  • int size()

Suggested steps to adding an ArrayList of Asteroids and finishing the project

  1. Create an ArrayList of type Asteroid. You may find the ArrayList slide presentation helpful.
  2. Now we'll modify the program so that when our space ship strikes an asteroid, the asteroid is removed from the ArrayList. Everytime an asteroid moves find the distance between that asteroid and the ship. Use processing's dist() function to find the distance between that asteroid and the ship. If the distance is less than 20 (or whatever value is appropriate for your game) remove the asteroid from the ArrayList. Otherwise, move and rotate the asteroid normally. See slide 47 of the Asteroids Parts 2 and 3 presentation for an example.
  3. Upload Asteroid.pde to your GitHub website. See slides 18 & 19 of the Asteroids Parts 2 and 3 presentation for two different ways to do this.
  4. Submit the same URL for your AsteroidsGame that you submitted for the previous assignment to Google Classroom.


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