©2007 Felleisen, Proulx, et. al.

8  Assignment

Etudes

Finish all the lab for this week and include it in your portfolio.

Abstracting with Interfaces and Function Objects Abstracting with Generics: Type Parameters

8.1  Problem

You will start this assignment with the given code. We will deal with two classes of data, Balloon and City. The goal will be to design common methods that work for both classes without changes.

Here is a brief inventory of the classes that are provided:

• City -- the information includes the name, state, zip code, latitude, and longitude

• Balloon -- the information includes the x and y coordinates of the center, the radius, and the color of the balloon

• AList<T extends ISame>, MTList<T extends ISame>, and ConsList<T extends ISame> that you have seen already in the lab. It includes the filter method that consumes an ISelect object and produces a list of all elements from this list that satisfy the given predicate.

• ISame<T> interface used for test comparisons

• ISelect<T> interface that represents a select predicate

• Examples -- the class with some examples of data and some tests already implemented

• TestHarness -- used for running the tests and reporting the test results

Later in the week we may add a number of new classes that will allow you to read the data from the console or from a GUI and display the graphical representation of the data.

1. Design the following classes that implement the ISelect interface:

   • RedBalloon -- that selects only the red balloons

   • SmallBalloon -- that selects all balloons with the radius smaller that the value given to the constructor.

   • Below40th -- that selects only the cities that are below 40th parallel of latitude

   • InState -- that selects only the cities in the given state.

   Make sure you test all these classes.

2. Design and run tests for the method filter in the classes that represent a list of <T> by using all four classes that implement the ISelect interface.

3. Add the following interface to your project:

   interface ShowMe<T>{
     public void display(T t);
   }
   

   Now design the following classes that implement the ShowMe interface:

   • PrintBalloon that prints the balloon data as a String to the system output

   • PaintBalloon that paints the balloon data in the graphics display

   • PrintCity that prints the city data as a String to the system output

   • PrintBalloon that paints the city as a small circle in the graphics display

4. Now design the method showAll in the classes that represent a list of <T>. Test is by using all four classes that implement the ShowMe interface.

5. Java Collections Framework -- the libraries we will soon use -- provides the following interface:

   public interface Comparator<T>{
     /* produce int < 0 if op1 is before op 2
      * produce 0 if op1 is the same as op2
      * produce int > 0 if op1 is after op2
      * in your desired ordering
      */
     public int compare(T op1, T op2);
   }
   

   Design the following classes that implement the Comparator<T> interface with methods that perform the following comparisons:

   • B1HigherThanB2 that determines whether balloon-1 is closer to the top than balloon-2

   • B1SmallerThanB2 that determines whether balloon-1 has smaller radius than balloon-2

   • C1BeforeC2 that determines whether the name of the city-1 is lexicographically before the name of the city-2

   • C1StateBeforeC2 that determines whether the state of the city-1 is lexicographically before the name of the city-2

6. Design the sort method for the classes that represent a list of <T> using the given instance of the Comparator. Test your program (and all helper methods) using all four of the classes defined above.