CS470/570 Assignment 1 (PS1): Running Scala
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Due: 11:55 PM, September 17, 2016.

How and What to Submit:

Homework for all problem sets will be submitted using the Canvas Assignments tool. Most homeworks will consist mainly of Scala files. For each assignment, you get to submit some text and some attachments. For many assignments, including this one, there will be no text (or just some pro forma line such as "Here is my homework for PS1"). There will be several attachments, consisting of Scala files and text files of various sorts, including runs of your program. For this assignment, attach the files FavMovie.scala , MyWeight.scala, ps1q2A.out, and ps1q2B.txt (or .doc or .html or …).

As we said in an announcement a few days ago, the file Resources > Scripts contain some helpful shell scripts for compiling and running Scala programs. The Scala compiler usually generates more class files than the Java compiler for a program of similar size. To hide this clutter away, create a bin directory below the directory your code appears in, then use the shell scripts scc and sca instead of scalac and scala. (These scripts work in any Unix system, including OS X and Linux. Windows users should choose scc.bat and sca.bat instead.)

Important: When a problem says that a certain output is to be produced, it is always phrased as precisely as possible, so that in producing your answer you know exactly what to print out. Make sure what is asked for is what your program produces, without any ruffles, flourishes, or improvements.

1 Download Scala to the computer you normally use, if you don't have it running already. (If a system administrator needs to do this, let me know.) Your first program should print out your favorite movie. Call this FavMovie.scala

2A Create an object MyWeight defined in a file MyWeight.scala. The object should have two constant public members

  1. MAX_WEIGHT: The maximum desirable weight in kilograms (a Doubledouble).
  2. MIN_WEIGHT: The minimum desirable weight in kilograms (a Double). This must be less than MAX_WEIGHT.

Of course, these don't have to be your actual target weight range.

The object should have a private var weight that is the current value of your (or some hypothetical person's) weight.

The object should have three public methods with this behavior:

  1. MyWeight.getWeight: Returns the current value of the private varible weight, your weight in kilograms. The type of getWeight is () => Double
  2. MyWeight.gain(w): Adds w to the value of weight. The argument w may be negative. If the value of weight ever falls below MIN_WEIGHT or rises above MAX_WEIGHT, gain should throw an exception. (You don't have to create a new class of exception, just evaluate throw new Exception(description string).) The "header" of gain is 
       def gain(w: Double): Unit

To the file MyWeight.scala add another object MyWeightApp that extends App. It should have the object MyWeight fluctuate up and down, gaining 5 kg and losing 4 kg every year. It should print out the lines: 

Start: 65.0 kg
Year 1: gain 5.0 lose 4.0
At year end: 66.0 kg
Year 2: gain 5.0 lose 4.0
At year end: 67.0 kg
Year 3: ...

until an exception is thrown. Your program should catch it and print: 

Maximum weight exceeded; weight = ...

The program should iterate for at most 50 years; after that you can eat whatever you want. If this happens without exceeding the maximum weight, the program prints 

Maximum time horizon exceeded; weight = ...

So no matter what it always prints the final value of weight.

The following subroutine may be of use in computing what to print out. If you want to use it, feel free; you can put the definition at the beginning of MyWeightApp 

  // String that represents a Double to 1 decimal digit of accuracy –
  def doubleApprox(d: Double): String = "%5.1f".format(d).trim

Run the program MyWeightApp and capture the output in a file ps1q2A.out.

2B What does the program do if MAX_WEIGHT = 75, MIN_WEIGHT = 40, weight = 77, and you execute MyWeight.gain(-1)? What should it do? Rewrite the specification so that it won't throw an exception in this case. You don't have to rewrite the code. Just turn in a concise specification of how the object MyWeight should behave. (There is no one correct answer to this problem. You have to think about what would make the object more useful.) You are allowed to assume additional public or private members for the object. You are not allowed to change MyWeight into a class or change MIN_WEIGHT or MAX_WEIGHT into vars. Put your revised specification in a Microsoft Word, text, or html file with the same general layout as problem 2A. Call it ps1q2B.html or .text or .docx.

Note double
"For double-precision floating-point number." If this is foreign terminology, just take it for granted that there is a good solid technical reason to make all floating-point numbers use 8 bytes instead of 4. (There isn't.) [Back]