Assignment 10: Interfaces

The goal of this assignment is to practice writing classes to implement an interface. There are two parts. You may be able to finish part 1 during the lab block.

As usual, make a new directory for this project and cd into it.

1. Revising the Set class

In the Set class you wrote for the previous assignment, you had choice--you could implement it using a character array or using a String. All of you chose to use a character array. To demonstrate that either would work, you will now re-implement set using a String instead. Do the following:

• Copy Set.java and SetDriver.java from the previous assignment's directory into your current directory. Rename Set.java as SetCharArray (and change the name of the class in the file).
• Make all the instance variables of SetCharArray private and all the methods public.
• Write the interface Set containing signatures of all the public methods of SetCharArray. Add a method elementNumber(int) that will return a certain character from the set (assuming that each element is ordered, from 0 to the size minus 1).
• Update SetCharArray:
  • Make it explicitly implement Set
  • It needs to have a method elementNumber(int).
  • You no longer can assume that any other has a char[] instance variable, so replace such references with calls to elementNumber
• Write a new class SetString which implements the interface Set but uses a String inside.
• Update the driver so as to give the user an option of which class to instantiate whenever you need a new set.

Hints: The String methods length(), charAt(int), and indexOf(String s). The last of these will tell you the location of the first occurrence of s in the receiver string, or -1 if it doesn't occur at all.

2. Shapes

Copy the files Shape.java and ShapeDriver.java from the class public directory to your directory for this assignment, and look at them in Xemacs.

In this part of the assignment, you will write classes for three types of shapes: Rectangles, right triangles, and isosceles triangles. They all should implement the Shape interface, that is, have methods for computing their area, computing their perimeter, and drawing a picture on the screen.

Write classes Rectangle, RightTriangle and IsoTriangle. Their draw methods should produce something like

**********
**********
**********

*
***
******
*********

     *
    ***
   *****
  *******
 *********
***********

Figuring out how to draw the triangles is the tricky part. You may discuss this with your classmates, but your code must be your own.

The constructors should query the user to get information about the dimensions for the shape.

As you go, update the driver so that it give the user the option to instantiate each shape class.

You also are responsible for documenting Shape.java.

3. Turn in

Create the script file as before (cat, rm, compile, and run)

 > a2ps -P sp (the name of the script file)

(This will print "two up", meaning two pages shown next to each other on one pice of paper. If you use a2ps on a Java file, it will format it nicely like in the handouts I've given in class. The command lpr works similarly except it does no formatting and doesn't print two up by default.)

Then turn in the hard copy by 5:00, Wed, Apr 6.