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Homework 3

Assigned Feb 12, due Feb 23

For all the programming assignments, be sure to follow the design recipe. Each problem asks you either to create a new class with some methods, or to add a new method to a class you've already written. For classes, you need to identify the names and types of the instance variables, then write each of the methods. For each method, go through the usual contract, examples, skeleton, inventory, body, test steps. I recommend writing the examples by using the tester library, as discussed in class on Feb. 11, so you can easily run all your tests and confirm that they all pass.

Be sure to choose meaningful names for methods and parameters, and watch for opportunities to re-use methods you, I, or the textbook have already written.

Also turn in a log of time spent and errors encountered in the assignment, with brief comments describing each error ("mismatched parentheses" is self-explanatory, but more complex errors might need more description). You may do this using the PSP forms, or simply by keeping track in a text file or on paper and turning it in.

• Starting with the Posn class I gave you, add several more methods:
  • addCoords, which given a Posn returns the sum of its x and y coordinates.
  • scalePosn, which given a Posn and a double, returns, a Posn whose x and y coordinates are those of the given Posn, multiplied by the double.
  • addPosns, which given two Posns, returns a Posn whose x and y coordinates are the sums of the x and y coordinates (respectively) of the parameters.
  • distance, which given two Posns, returns the straight-line distance between them, using the formula
    √((x₁-x₂)² + (y₁-y₂)²)
• Develop a class Book which represents a book, with a title, author, year of publication, and ISBN. It should have at least the following methods:
  • a constructor
  • "getter" methods (but no "setters") for all the instance variables (the conventional names are getTitle, getAuthor, etc.). Make your instance variables private.
  • toString, which given a Book, returns a nicely formatted, human-readable String form of it.
• Develop a class Date which represents a date (day, month, and year). For simplicity, we'll pretend that a year is 360 days long, with 12 months of 30 days each (we'll make this more realistic in a week or two). It should have at least the following methods:
  • a constructor
  • "getter" methods (but no "setters") for all the instance variables. Make your instance variables private.
  • toString, which given a Date, returns a nicely formatted, human-readable String form of it
  • dayInYear, which given a Date, returns how many days it has been since last New Year's Eve (for example, Jan. 1 would be day 1; Feb. 4 would be day 34; etc.)
  • extra credit: daysLater, which given a Date and a positive integer, returns a new Date that many days later.
    (I thought at first you couldn't do this with what you know now, but in fact you can if we assume 30-day months.)
• Develop a class RunnerLog which represents an entry in a runner's log book. Each entry has the date of the run, how many miles, how many hours, and comments. It should have at least the following methods:
  • a constructor
  • "getter" methods (but no "setters") for all the instance variables. Make your instance variables private.
  • toString, which given a RunnerLog, returns a nicely formatted, human-readable String form of it
  • avgSpeed, which given a RunnerLog, returns the average running speed in miles per hour for that run.
  • addComment, which given a RunnerLog and a String, returns a new RunnerLog just like it, but with the String added onto the end of whatever comments were already there.

What to Turn In

You should end up with several classes: Posn, Book, Date, and RunnerLog, as well as a test class for each, with names like PosnTest, BookTest, DateTest, and RunnerLogTest. I recommend keeping all of these in one BlueJ project (with a name like "Homework3"); zip up the whole folder and attach it to an e-mail to me. If you've entered your time and error logs using the on-line forms, I've already got them; if not, e-mail me your log files.

Grading standards

Programming:

Note: I won't actually grade every one of these methods, but a representative sample; the rest are for practice. If I were to grade them all, the points would look something like this:

General skills:

Total:         depends on how many methods and classes I actually grade