CS 201 Advanced Object-Oriented Programming Lab 4 - Asteroids, Part 2 Due: February 24/25, 11:30 PM

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1 CS 201 Advanced Object-Oriented Programming Lab 4 - Asteroids, Part 2 Due: February 24/25, 11:30 PM Introduction to the Assignment In this lab, you will complete the Asteroids program that you started last week. In writing this program you will gain experience creating a superclass and extending it. In particular, you will be creating an Asteroid class, which shares many features with the Ship class you wrote last week. An Asteroid is a polygon that can be rotated and move across the screen in any direction. There are some differences, however. An Asteroid is a more complex shape than just a triangle. While it can be oriented in any direction, it does not change its orientation after creation. Also, it travels in a straight line at a constant speed. Here are some snapshots from this program: Here is the starting screen. The ship is in the center and pointing up. The asteroids start in random locations and move in straight lines, but in random directions. If an asteroid hits the ship, the ship will disappear. The user can shoot with the space bar. Bullets will go in the direction that the spaceship is pointing. If a bullet hits an asteroid, the asteroid will disappear. 1

2 Java Assert Statements Java has support for assertion checking. Java does not distinguish between preconditions, postconditions, and invariants. Instead it provides one statement, an assert statement, and a virtual machine argument that either inserts assertion checking or turns it off. Assert statements are excellent ways to check that the assumptions you have on the way your program works are correct. Thus, for each assumption that you want to check, you would add an assert statement. If assertion checking is enabled and an assertion is violated, Java will produce a stack trace identifying the location of the assertion failure. Liberal use of assertion checking is an excellent way to find errors close to where the problematic code is. By default, assertions are disabled at runtime to improve performance of the executing code. To enable assertion checking, you must pass the "-ea" argument to the Java virtual machine. You can set Eclipse so that -ea argument is used by default whenever you run your program from Eclipse. To do that, open the Eclipse menu and select Preferences. In the window that appears, open Java in the left column and select Installed JREs. Select the JRE that is used and click the Edit button. In the window that pops up type -ea in the Default VM Arguments field. Click Finish and then Ok. For more details on assertion checking in Java, please see Oracle s documentation on assertion checking at You should get into the habit of using assert statements to check your assumptions. If you use them well, you will find them to be a powerful debugging tool. The Program Design In addition to the classes from last week, this lab also includes: Asteroid - a class to manipulate the asteroids flying around the display Bullet - a class to manipulate the bullets the ship shoots to destroy the asteroids. AsteroidsGameShape - a superclass of Ship, Asteroid and Bullet that captures the similarities between these shapes, how they are drawn, how they move, etc. TransformCalculator - a class that I provide to you that does the trigonometry necessary to determine where the various shapes are on the screen when they are rotated and moved. You will need this to determine when 2 shapes collide. You can download TransformCalculator.java from the course website. This class is completely written for you. YOU SHOULD NOT CHANGE IT! You will also be using the Point2D.Double class that Java provides that you are not yet familiar with. This class provides an x, y pair to identify a location in a coordinate system. Writing the Program You should download TransformCalculator.java from the course website and import it into your project. YOU SHOULD NOT CHANGE IT. Step 0: Copy your Eclipse project In Eclipse, select your Asteroids project. Right-click on the project and select Copy. Then right-click and select Paste. Change the name of the project to AsteroidsPart2. Step 1: Create the AsteroidGameShape superclass One of the main parts of this lab is to create the Asteroid class. For lab preparation, you should have compared the behavior of your ship with the behavior you want asteroids to happen to determine what functionality you can move into a shared superclass. For this step, you should create that superclass, called AsteroidGameShape and move things there from the Ship class that are appropriate for both the ship and the asteroids. Don t create 2

3 the Asteroid class yet, just divide the current functionality of Ship into these two classes: AsteroidGameShape and Ship. At the end of this step, your program should behave exactly the same as it did after last week s lab, but the code should be different. Step 2: Add asteroids Now, create your Asteroid class as another subclass of AsteroidGameShape. Add to Asteroid anything specific to asteroids. Be sure that the speed of your asteroid is at least 2 pixels per frame. Then, go to the AsteroidGames class and construct an asteroid. Start with just one asteroid. Add the code do paint and move the asteroid. Try it. Do you have an asteroid flying around? If not, maybe you need to change what is in the AsteroidGameShape. Maybe more of the Ship class should be moved into the new superclass, or maybe you ve moved too much already. Think about similarities and differences to determine exactly what goes into each of these three classes. Once that works, change AsteroidsGame to hold an array of asteroids and create a bunch of asteroids that all move around the screen. You can create your asteroids at fixed locations and with a fixed rotation. For extra credit, generate them in random locations (but not too close to the Ship s starting position) and a random rotation. Step 3: Detect collisions between asteroid and space ship If the ship collides with an asteroid the ship should disappear from the screen. You should define a collideswith method in your AsteroidGamesShape class that takes another AsteroidsGameShape as a parameter. You should call this method in AsteroidGame s nextframe method, once for each asteroid, checking to see if it has hit the ship. The simplest way to detect collisions (and what I recommend that you do) is to get the bounding box for the shape. A bounding box is the smallest upright rectangle that encloses the shape. The type of a bounding box is Rectangle2D, which is defined by Java. It provides a method: public boolean intersects (Rectangle2D r) So, if you have the bounding box of both the ship and an asteroid, you can call this intersects method. If it returns true, the two shapes have collided (or at least we will claim that they have). Here is the intersects method that you should add to AsteroidGameShape: /** * Determine if this shape has collided with another shape othershape the shape to compare to true if there was a collision */ public boolean collideswith(asteroidgameshape othershape) {! Rectangle2D bounds = TransformCalculator.calculateRotatedBounds(!!! shape.getbounds2d(), left, top, rotation);! Rectangle2D otherbounds = TransformCalculator.calculateRotatedBounds(!!! othershape.shape.getbounds2d(), othershape.left, othershape.top,!!! othershape.rotation);! return otherbounds.intersects(bounds); } After inserting this method, you should call this method from AsteroidGame s nextframe method, once for each asteroid. If the ship is hit, initially just use System.out.println to display a message on the console. 3

4 Once you see that the collisions are detected, remove the println, add an instance variable in the Ship to remember that it has been destroyed and define a method destroy() in Ship to set this variable, and a method isdestroyed() to return whether the ship has been destroyed. The ship should no longer be displayed on the screen. Step 4: Add controls to shoot bullets It s no fun if the asteroids always win! The user types the space bar (KeyEvent.VK_SPACE) to shoot a bullet. The bullet should start at the nose of the ship and travel in the same direction that the ship is facing. It should move faster than the ship. Add the following method to your Ship class to determine where the tip of the Ship is: public Point2D.Double getgunpoint() {! return TransformCalculator.transform(new Point2D.Double(0, -HEIGHT/2),!! left, top, rotation); } You will need to create a new class called Bullet. Notice that it is also an AsteroidsGame- Shape! However, it moves differently than the others, because the bullets do not wrap around. The ship should not be able to shoot bullets after it is destroyed. Step 5: Detect collisions between bullets and asteroids This is very similar to the collision detection that you already did for step 3. You will need to check each bullet against each asteroid. Also, when you destroy an asteroid, not only should it disappear from the screen, but it also shouldn t be able to collide with the ship. (Sounds obvious, right?) A bullet should only be able to destroy 1 asteroid. Extra credit ideas You should not work on extra credit until you have all the steps above working well and you have added comments and used good style. You will not receive extra credit points if you have not done a good job on the basic assignment. Simple: Create asteroids at random locations and with a random rotation, add a button to allow the user to restart the game, add another kind of asteroid with a different shape, allow the user to hyperspace the ship, display Game Over if the ship is destroyed or all asteroids are destroyed. Moderate: Display a score, introduce multiple levels Grading 10 Pre-lab worksheet 15 Step 1: Create the AsteroidGameShape superclass. 15 Step 2: Add asteroids 10 Step 3: Detect collisions between asteroid and ship 10 Step 4: Add controls to shoot bullets 4

5 10 Step 5: Detect collisions between bullets and asteroids 15 Comments (including javadoc comments) 15 Style 5, 10 Extra credit (simple, moderate respectively) Turning in Your Work Create a jar file, being sure to include your source code. To make your jar file doubleclickable, do the following. After telling Eclipse which files to include in the jar file (in the Jar File Specification window), click Next instead of Finish. Click Next again in the Jar Packaging Options window. At the bottom of the Jar Manifest Specification window, there is a field for Main class. Either enter the name of your class that contains the main method (AsteroidsGame) or click the Browse button to find your class. Then, go to ella. Click on COMSC 201 in the toolbar menu across the top. Then click on Assignments in the left column. Click the submit link for this assignment. Click the Add Attachment button. Use the Browse button to upload a local file. You should submit your jar file. Click Continue. Then click the Submit button. 5