Assignment 5: World programs: ZType

Goals: Design an interactive program bringing together all of the material we have covered so far. Learn to use and test randomness.

5.1 Instructions

This is a partner assignment.

Make sure you follow the style guidelines that we enforce. For now the most important ones are: using spaces instead of tabs, indenting by 2 characters, following the naming conventions (data type names start with a capital letter, names of fields and methods start with a lower case letter), and having spaces before curly braces.

You will submit this assignment by the deadline using the online submission system. You may submit as many times as you wish. Be aware of the fact that close to the deadline the system may slow down to handle many submissions - so make sure to submit at least a few minutes before the deadline.

As always, be sure to follow the Design Recipe and avoid accessing fields of fields, getters, type-checking and casting. Dynamic dispatch is your friend!

The submissions will be organized as follows:

• Assignment 5: All the files needed for your game, in one .zip file

Practice Problems

Work out these problems on your own. Save them in an electronic portfolio, so you can show them to your instructor, review them before the exam, use them as a reference when working on the homework assignments.

• Problem 20.2 on page 296

• Problem 20.6 on page 305

• Problem 20.6 on page 305

• Problem 20.8 on page 306

• Problem 20.9 on page 306

• Problem 21.1 on page 312

• Problem 21.3 on page 312

• Problem 21.4 on page 315

• Problem 21.5 on page 320

• Problem 21.6 on page 320

• Problem 21.7 on page 320

The javalib library

The javalib library provides the support for the design of interactive games and creating images composed by combining geometric shapes as well as image files. See The Image Library for more information.

To use the library, download the javalib file above and add it to your project the same way you have added the tester library.

At the top of the .java file where the library is used, add the following import statements:

Note that you should not use any mutation (or any other techniques that we have not covered in class) in this assignment.

ZType

Implement the game ZType. ZType is a typing game where the player must type words presented on the screen quickly to destroy them before they reach the bottom of the screen. Here are some tasks to help you get started:

1. Review the DotAnimationExample file shown in class which is a world program. You will also need to review the The Image Library documentation mentioned above. Make sure you understand how the animation works.

2. Decide if you need to define any constants for the game. These are things that do not change throughout the life of the program, such as height and width of the game’s background. Review Lecture 10: Customizing constructors for correctness and convenience about defining constants.

3. Design the ZTypeWorld class. This should extend the World class from javalib. What fields should be included in this class? The field(s) of this class will represent what can change in the world program.

   Hint: The ILoWord definition from Assignment 3 should be helpful!

   Don’t forget the templates, especially those methods of fields!

4. Design the makeScene method which is required in the ZTypeWorld class. This will draw the current state of the world. Make sure to test this on at least three different examples of world states.

5. In a Utils class, design a method to produce a String of six alphabetic characters. To keep things simple the words in the game do not have to be real English. Instead, your method should use six randomly chosen characters. An accumulator method may be helpful for building these words.

6. Decide which events your ZTypeWorld class should handle.

   • Does the game need to respond to the passage of time? Then you need to override onTick in the ZTypeWorld class. A new random word should be added to the list of words periodically, so this is something that onTick will need to handle (among other things). You will also need to figure out how often a new word should be added. Adding one at each tick would be too fast!

   • Does the game need to respond to key presses? Then you will need to override one of the key handler methods.

   • Review the The Image Library to see the documentation for onTick and to see which key handler methods are available.

   • Hint: Some of the methods that you implemented in Assignment 3 will be useful as helpers to your event handlers.

7. Your game should end if a word reaches the bottom of the scene. There should be a final scene indicating that the player has lost the game. Study The Image Library documentation for information about ending world programs.

If you decide to implement any extra features, make sure to document them well. Remember – you will be graded for your program design, not making a cool video game. So whatever you add, make sure it’s well-designed. But have fun with it, too!

A note about randomness

There are two ways to generate random numbers in Java. The easiest is to use Math.random(), which generates a double between 0 (inclusive) and 1 (exclusive). You can multiply this number by some integer to make it bigger, then coerce to an int to produce a random integer in the range you wish. However, this is not easily testable: you’ll get different random values every time.

The better way to generate random numbers is: First, import java.util.Random at the top of your file. Next, create a new Random() object, and use its nextInt(int maxVal) method, which will give you a random integer between zero (inclusive) and maxVal (exclusive).

• One of them, to be used for testing, should take in a Random object whose seed value you specify. This way your game will be utterly predictable every single time you test it.

• The second constructor should not take in a Random object, but should call the other constructor, and pass along a really random object:

  import java.util.Random;

  import javalib.funworld.*;

  class YourWorld extends World {

  Random rand

  // The constructor for use in "real" games YourWorld() { this(new Random()); }

  // The constructor for use in testing, with a specified Random object YourWorld(Random rand) { this.rand = rand; ... }

  }

  Now, your tests can be predictable while your game can still be random, and the rest of your code doesn’t need to change at all.

Submission notes