©2009 Felleisen, Proulx, et. al.

6  Abstracting with Function Objects

Portfolio Problems

1. Include the solution of the Lab 6 in your portfolio.

2. Add a few more examples of tests in the Examples class.

3. Define a class ImageSmallerThanAndGivenKind that implements the ISelect interface with a method that selects image files that are small and of the given kind. Allow the user to decide how small should the images be (measuring the size as the number of pixels in the image) and allowing the user to choose the kind of images that should be selected. (All selected images must be of the same kind.)

   Test your class definition on several examples before you use it in your allSuch, anySuch, and filter methods.

4. Add test cases that will test the methods allSuch, anySuch, and filter with several instances of the ImageSmallerThanAndGivenKind predicate.

Pair Programming Assignment

6.1  Problem

During the lectures we have designed the method filter for a list of Books, selecting books written by the given author and books that cost less than the specified price.

1. Define the class Book and the classes that represent a list of Books, as well as the ISelect interface and the needed classes that implement it to select a given author, and to select a book cheaper than the given price. Make sure you test the classes that implement the ISelect interface.

2. Define the methods filter, orMap, and andMap as we have done in the lectures.

   Note: Until now you are just writing up the lecture notes as a working program.

3. Define the following interface in your project:

   // to represent a method that determines whether 
   // book b1 comes before book b2
   interface Ordering{
     public boolean isBefore(Book b1, Book b2); 
   }
   

   Define at least two classes that implement this interface. (You may order the books by the price, the length of the book title, author’s names, etc.)

4. Design the method sort for the classes that represent a list of Books that uses an instance of a class that implements the Ordering interface to define the appropriate ordering of the books and produces the list in the correctly sorted order.

5. Design the method isSorted for the classes that represent a list of Books that uses an instance of a class that implements the Ordering interface to determine whether a list of Books is sorted correctly.

   Note: Remember the one task one method rule.

6. Design the method merge for the classes that represent a list of Books that merges a sorted list with another sorted list, producing a list that has all elements of both lists — again in a sorted order. An instance of a class that implements the Ordering interface determines the ordering of both the original two lists and the resulting list.

6.2  Problem

You will work with a binary search tree that represents a collection of Book objects. It should be very similar to the binary search trees that had only integer data.

The class diagram on the next page should help you.

1. Define the classes that represent a binary search tree of Book objects as shown in the class diagram above.

2. Define the method insert that inserts a new Book into the binary search tree, using the Ordering already defined for this tree.

                    +---------------------+
                    | abstract class ABST |
                    +---------------------+
         +----------| Ordering order      |
         |          +---------------------+
         |                 / \
         |                 ---
         |                  |
         |      -----------------     
         |      |               |
         |   +------+   +------------+
         |   | Leaf |   | Node       |
         |   +------+   +------------+
         |              | Book data  |--------+
         |              | ABST left  |        |
         |              | ABST right |        |
         |              +------------+        |
         |                                    v
         v                                 +---------------+
   +------------------------------------+  | Book          |
   | Ordering                           |  +---------------+
   +------------------------------------+  | String title  |
   | boolean isBefore(Book b1, Book b2) |  | String author |
   +------------------------------------+  | int price     |
                                           +---------------+
   

3. Define the method getFirst that produces the first Book in the binary search tree (as given by the appropriate Ordering.

   In the Leaf class this method should have the following body:

   throw new RuntimeException("No first in an empty tree");
   

4. Define the method getRest that produces a new binary search tree with the first Book removed.

   In the Leaf class this method should have the following body:

   throw new RuntimeException("No rest of an empty tree");