ITEC 380 2019fall ibarland

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structs
hw04

Due:
Sep.27 (Fri) at the start of class, D2L and hardcopy.
Your submitted file should be named “hw04.rkt”, plus any .java files.

Standard instructions for all homeworks:

• Your name, the assignment-number, and the URL of this assignment must be in a comment at the start of the file.
• Any code which results in syntax errors will generally not earn more than 50% of the points-possible. For grading, I will ignore any commented-out code (unless the problem is explicitly asking for commented-out code, ’course).
• If your hardcopy is more than 1page, it must be stapled.
• Format well (in particular, each open-paren should be preceded by a space or start-of-line, for now).

(This is the completion of hw04a, from D2L.) Consider the following information, which might be part of a sports-simulation:

A team is:

• a name (non-empty string), AND
• an offense rating (real number), AND
• a defense rating (real number).

1. (5pts) Give a data definition (including examples of the data, and the template for any function which processes a team), as per steps 1-3 of the design recipe. Give at least three examples of a team.

2. (5pts) We’ll say one team is “greater” than another if its offense is higher than the other’s defense, and its defense is higher than the other’s offense. Write the function team>? to implement this. Follow all the steps of the design recipe¹. As always, be sure to think about enough test-cases to cover the interesting situations (half of the pts). (In this case, six or seven should suffice, if they each cover a different situation.)

Familiarize yourself with the arcade game Galaga, such as this example. We will write a simplified version which only needs to deal with: aliens parading back and forth, diving (in an angled-but-perhaps-straight line), the player's ship ("ship"), and the missiles (both the player's and the alien's). It does not need to deal with: score, having more than one level, number-of-lives, or the “entrance” phase of the aliens.

There are three types of things (objects) which our program will need to model: ships, missiles, and aliens.

3. (10pts) Give a data-definition for a missile in Java — that is, a class Missile. Include examples of the data, and a template for any Missile-processing function(method). As always, be sure to mention the units for any fields, as needed.

   hints: General tips for deciding what fields an object needs:

   • Imagine a friend is playing your game, and paused+saved it mid-play. When they later re-open that save-file, what info needs to be in there about a particular ball, so the program can exactly re-construct the ball how it was the moment your friend saved it?

   • Do not include information that is not part of the object itself.

   • Do NOT include information which never changes (is “invariant”) for a class. For example, if all instances of an object are always the same color, you wouldn’t have a field for the color. (You wouldn’t want 1000 objects, each with their own field, which all necessarily hold the exact same value.)

   • Sometimes x,y coordinates suffice to describe something’s position. However, sometimes more context might be needed. For example: what is the latitude and longitude of Virginia?

     On a related note: For a problem below, you might be using place-image, which places the center of an image at specified coordinates. If your internal representation is consonant with libraries you use, it can make things a smidgen easier.

   Since this is Java, you will also need to create: a constructor, equals(Object), and hashCode() (and optionally, toString()). These will all be boilerplate methods similar to lecture’s Book.java.

   Note: You do not need to create getters/setters (and moreover, you should not). Moreover, for this homework and course, we will use immutable data, so you should not reassign to any fields²

4. (5pts) Now write a Java Missile method Missile move() which returns a Missile whose position is changed, to account for its movement over one frame (one “tick”). This function should not worry about collisions.
   • The method does not take any inputs (beyond the ball being moved).
   • You will not modify any fields, but instead return a new object.
   • Your Java unit-tests can be simple asserts in the same class-file, (as in Book.java), for full credit. Alternately, if you want, you can use JUnit and a separate test class.

     enabling assertions in Java: When running your program, the JVM’s default behavior is to entirely ignore assertions (!?!). You should run with³ java -enableassertions someClassName, or convince your IDE to do this.

The remaining functions are to be in racket (not Java); the Java version is just to compare and emphasize how similar the immutable-Java and racket programs will be.

5. (5pts) Give racket data-definitions, examples-of-data, and template for missile, ship, and alien. For aliens, you should handle the fact that it might be in the middle of a dive (or not).

   Note: Although full racket does support struct-inheritance, we will not use it here

6. (5pts) Write move-missile in racket, which behaves the same as Missile#move()⁴.
7. (5pts) Write ship-handle-key : ship, key-event? -> shippaddle, which updates a ship in response to a keypress.
8. (5pts) Drawing functions:
   1. Write the function draw-missile : missile, image -> image, which takes a missilebrick and a “background” image, and returns that background image with the missilebrick drawn on top of it.

      hint: place-image is a handy function; it is similar to overlay/xy except that it crops the result to the background.

      hint: For test-cases, include drawing a missile that is: (a) near the center of a small image; and (b) one that is mostly off the left-edge but has just a few pixels showing.

      Note: Here’s an image you can (modify to) use in your test-cases, in addition to a solid rectangle or whatever else you might choose: house-with-flowers.rkt. If you place this file in the same directory as other functions, you can just (require "house-with-flowers.rkt"), and then use its exported id (house-with-flowers, coincidentally). You don’t need to print this file, but do submit it on D2L so that I can run your program.

   2. Write draw-ship, similarly.
   3. Write draw-alien, similarly.

      Note: My own version of draw-alien took in a second parameter — the "fleet's" location. Your version does not need to do this.

      Note: If you want a diving-alien to be drawn differently — at an angle perhaps — you may, but that complication is certainly not required.

   I suggest using simple shapes (like mere rectangles) for all your drawing-functions for the game. You are welcome to be much fancier, though it won’t earn you additional credit. You are welcome to use jpg/png/bitmaps, but make sure you have the legal right to copy them — e.g. from sites like classroomclipart.com or libraries like planetcute . Please site your source, of course!

9. (0pts) Start writing, or at least thinking about, move-alien. This function is tricky because of diving. My version, like draw-alien, will take in an additional parameter: the fleet location.

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