CSC 171
Homework 6

Assigned Mar 4, due Mar 13

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 StringList example given out in class, write the following methods:
  • concatAll, which takes no explicit parameters and concatenates all the Strings in the list into one big long String.
  • maxLength, which takes no explicit parameters and computes the maximum length of Strings in the list. You may want to use the built-in Math.max method, or you can do it yourself with conditionals.
  • contains, which takes in a String and tells whether or not that String appears as one of the elements of the StringList.
  • countMatches, which takes in a String and tells how many times (possibly zero) that String appears as an element of the StringList.
• Define an IntList class analogous to StringList but with each element an int. Write the following methods:
  • length and add, by analogy with the corresponding methods in StringList.
  • addUp, which takes no explicit parameters and returns the sum of all the numbers in the IntList.
  • multiply, which takes no explicit parameters and returns the product of all the numbers in the IntList.
    (Hint: the "right answer" for an empty list may not be what you think at first.)
  • anyOver100, which takes no explicit parameters and returns whether any of the numbers in the list are over 100.
  • allOver100, which takes no explicit parameters and returns whether all of the numbers in the list are over 100. (See previous hint.)
  • countOver, which takes an int parameter and tells how many of the elements of the IntList are larger than this number.
  • largest, which takes no explicit parameters and returns the largest number in the list.
    (Hint: What, if anything, is the "right answer" for an empty list? You may need to write a "helper" function.)
• Define a BookList class analogous to StringList and IntList, but with each element a Book (from homework 3). Write the following methods:
  • length and add, by analogy with the corresponding methods in StringList
  • anyBefore, which takes in a number and tells whether any of the books was published before that year.
  • avgYear, which takes no explicit parameters and returns the average of the publication dates of all the books in the list. Hint: You'll probably need a "helper" method.
• After the March 6 lecture, go back to the StringList class and add the following methods:
  • addToEnd, which takes in a String and returns a StringList with that String added as the last entry. Hint: This will be trickier than add, which added an entry at the front.
  • lengths, which takes no explicit parameters and returns an IntList with the same number of elements as this StringList. Each element of the resulting IntList should be the length of the corresponding element of the StringList.
    For example,

    checkExpect (new ESL().add("fnord").add("abc").add("beeblebrox").lengths(),
                 new EIL().add(5).add(3).add(10));
    

  • prefixEach, which takes a String and returns a StringList with the same number of elements as this. Each element of the resulting StringList should be the given String concatenated with the corresponding element of this.
    For example,

    checkExpect (new ESL().add("fnord").add("abc").add("beeblebrox").prefixEach("xyz"),
                 new ESL().add("xyzfnord").add("xyzabc").add("xyzbeeblebrox"));
    

  • append, which takes a StringList and returns a StringList containing all the elements of this, followed by the elements of the parameter StringList.
    For example,

    checkExpect (new ESL().add("abc").add("f").add("r").append(
    		new ESL().add("xyz").add("fnord")),
    	     new ESL().add("xyz").add("fnord").add("abc").add("f").add("r"));
    

  • removeAll, which takes a String and returns a StringList containing all the elements of this that do not match the given String.
    For example,

    checkExpect (new ESL().add("abc").add("f").add("abc").add("abc").add("g").add("xyz").removeAll("abc"),
                 new ESL("f").add("g").add("xyz"));
    

  • removeFirst, which takes a String and returns a StringList containing all the elements of this, minus the first match (if any) of the given String. If the String parameter doesn't appear at all, return the StringList unchanged.
    For example,

    checkExpect (new ESL().add("abc").add("f").add("abc").add("abc").add("g").add("xyz").removeFirst("abc"),
                 new ESL().add("abc").add("f").add("abc").add("g").add("xyz"));
    

    (Remember, add adds things at the front, so the last thing added is the "first" thing in the list.)
  • removeFirstN, which takes an int n and a String, and returns a StringList containing all the elements of this, minus the first n matches of the given String. If the String parameter doesn't appear at all, return the StringList unchanged. If it appears n or fewer times, remove all of them.
    For example,

    checkExpect (new ESL().add("abc").add("f").add("abc").add("abc").add("g").add("xyz").removeFirstN(2,"abc"),
                 new ESL().add("abc").add("f").add("g").add("xyz"));
    

    (Remember, add adds things at the front, so the last thing added is the "first" thing in the list.)
• Likewise, go back to the LogList class and add the method removeBefore, which takes in a number and returns a BookList containing all the elements of the original BookList except those published before that year.

What to Turn In

You should end up with classes StringList, IntList, BookList, two subclasses of each of those, a test class for each, and the Book class copied from homework 3. I recommend putting all of them in one BlueJ project. Zip them up 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

Pretty much the same as the past few assignments.