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Homework 9

Assigned April 13, due April 27

Before you start writing any code for this assignment, please turn in a project plan with estimated lines of code, hours, and defects. After you've finished, compare the actual lines of code, hours, and defects (from your time and defect logs) with your initial estimate. The estimate will probably be far from reality, but that's how you learn to make more accurate estimates next time. I recommend using the PSP forms.

As always, be sure to follow the design recipe. 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.

• Starting with the Date class from homework 3 and 4,

  • modify the monthName method (or write it if you didn't before) so that it uses an array or an ArrayList instead of a huge "if" statement. (The toString method should still call monthName. If you prefer, you could drop the monthName method entirely and just refer to the array or ArrayList from within toString.)
  • modify the dayInYear method (or write it if you didn't before) so that it uses an array or an ArrayList to keep track of the number of days in each month.
  • modify the daysLater method (or write it if you didn't before so that it handles month lengths and both positive and negative numbers of days "later".

• The built-in String class has a lot of predefined methods, but not everything you might conceivably want to do with a String. Chapter 10 of the Gee book shows how to write recursive methods on Strings, similarly to what we did with lists in Homework 7:

  public static whatever doSomething (String s)
    {
      if (s.length() == 0)
      {
        return // whatever the answer is for the empty string
      }
      else
      {
        // s.charAt(0)           the first character in the String
        // s.substring(1)        the rest of the String
        // doSomething (s.substring(1))   the answer for the rest of the String
        return // something involving s.charAt(0) and doSomething(s.substring(1))
      }
    }
  

  Write a Dummy class with the following methods:

  • Write a static method countVowelsRecursively which takes in a String and returns the number of vowels ("a", "e", "i", "o", and "u") in it. It should work recursively, like the above example.
  • Write a static method countVowelsWithWhile which does the exact same thing, but it uses a while loop instead of recursion.
  • Write a static method countVowelsWithFor which does the exact same thing, but it uses a counter-based for loop instead of recursion or a while loop.

  • The scramble method of homeworks 7 and 8 was sort of unnatural: in a real newspaper word-scramble game, you scramble the letters in one word to get a list of words rather than scrambling a list of words to get a list of lists of words. Write a static method scramble that takes in a single String and returns a StringSet or StringList containing all the possible reorderings of the characters in that String. (You may use any version of StringSet or StringList that you've previously written, whether from Homework 7 or Homework 8, or you could even just use a Set<String>.)

  • A common task in computer science is pattern-matching: given a pattern, ask whether a particular string matches it. In our pattern language, a "?" stands for "any single character," while "*" stands for "any zero or more characters." For example, the pattern "c?t" would match "cat" and "cut" but not "colt", "cats", or "dog". Similarly, the pattern "cat*" would match the strings "cat", "cats", "catastrophe", etc. but not "caltrop" or "dog". The pattern "a??a*r" would match "abbatoir", "akbar", and "araaar", etc. but not "almoner", "alakazam", or "fnord". Write a static method matches that takes in two Strings -- a pattern and a target -- and returns a boolean indicating whether the target matches the pattern. Note that the "special" characters "?" and "*" are special only when they appear in the pattern; if they appear in the target, they should be treated as ordinary characters.

Grading standards

Pretty much the same as the past few assignments.