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Drawing Shapes: Generalizing the Problem

In this section, you'll write a program that displays the data in a histogram form, like this:

with the same resizing behavior as before:

In other words:

• display the original points (in black)
• display green lines connecting the points
• display the data in the form of a histogram by drawing red rectangles

Because we're displaying rectangles based at the x axis (where y = 0), we're including a larger region of world coordinate space, so the points appear to move upward in the window, compared with the results of the last part of this assignment.

We'll be using inheritance and polymorphism to simplify the job. We've done all the hard work in Part A -- this should be quite a bit simpler, if you've done things properly in Part A.

To implement this, you will need refer to the Specification again;  we'll be implementing more of the classes specified therein.

Here's What To Do:

1. Write the shapes.Line and shapes.Rectangle classes.

   Bear in mind:

   • Both Line and Rectangle will extend class Shape. 
   • Ignore the FilledRectangle class; that will be used in the next section.
   • Augment your ShapesTest class to use the above classes to produce the above results.

   Once you've implemented these classes, and augmented the ShapesTest class appropriately, you should see results like the above images.

   How will you draw the histogram?

   Hints:

   • Note that the points are all spaced evenly in the x direction, so you can figure out the width of each rectangle quite easily from the x coordinates of the points. Each point should be centered in its corresponding rectangle.  The height of the rectangle should be determined by recognizing that the base of the rectangle is on the x axis (where y = 0), and the top of the rectangle should intersect with the corresponding point.
   • Think about the order in which you need to draw the three sets of graphical objects so that they display correctly.  This will be reflected in how you specify the shapes in your m_shapes array in the ShapesTest class.
   • You should not have to change any of the classes implemented in Part A in order to get this to work. If you think you must make a change to them, you're probably doing something wrong!  Try to figure out what you did wrong, and correct it, highlighting what you changed. I want to see what you did to make this work!

2. Write the shapes.FilledRectangle class

   Here, we will modify your program to display the histogram slightly differently:

   

   Notice that our rectangles are now filled with a different color. This is where the FilledRectangle class comes in:

   • Implement the FilledRectangle class, per the specification.
   • Modify your ShapesTest class to use the FilledRectangle class, in place of the Rectangle class, to produce the above results.
   Notes:

   • There should be no need to change any other classes to make this work.
   • The implementation of FilledRectangle should be relatively simple. (A lot of the work is already done in the Rectangle class.)
   • The changes to ShapesTest should be simple -- just change the Rectangles referred to in the m_shapes array to FilledRectangles.

3. See Whether You've Implemented Things Correctly:

   Change the contents of the m_shapes array to the following:

   public static Shape[] m_shapes = { new FilledRectangle(-4.999999999999994, 95.0, 5.000000000000006, 105.0, Color.cyan, Color.blue), new FilledRectangle(-100.10565162951535, 25.901699437494752, -90.10565162951535, 35.901699437494756, Color.cyan, Color.green), new FilledRectangle(-63.77852522924732, -85.90169943749473, -53.77852522924732, -75.90169943749473, Color.cyan, Color.red), new FilledRectangle(53.77852522924729, -85.90169943749476, 63.77852522924729, -75.90169943749476, Color.cyan, Color.magenta), new FilledRectangle(90.10565162951536, 25.901699437494717, 100.10565162951536, 35.90169943749471, Color.cyan, Color.orange), new Line(6.123233995736766E-15, 100.0, -58.77852522924732, -80.90169943749473, Color.blue), new Line(6.123233995736766E-15, 100.0, 58.77852522924729, -80.90169943749476, Color.blue), new Line(-95.10565162951535, 30.901699437494752, 58.77852522924729, -80.90169943749476, Color.green), new Line(-95.10565162951535, 30.901699437494752, 95.10565162951536, 30.901699437494717, Color.green), new Line(-58.77852522924732, -80.90169943749473, 95.10565162951536, 30.901699437494717, Color.red), new Line(-58.77852522924732, -80.90169943749473, 6.123233995736766E-15, 100.0, Color.red), new Line(58.77852522924729, -80.90169943749476, 6.123233995736766E-15, 100.0, Color.magenta), new Line(58.77852522924729, -80.90169943749476, -95.10565162951535, 30.901699437494752, Color.magenta), new Line(95.10565162951536, 30.901699437494717, -95.10565162951535, 30.901699437494752, Color.orange), new Line(95.10565162951536, 30.901699437494717, -58.77852522924732, -80.90169943749473, Color.orange), new Line(-150.0, 0.0, +150.0, 0.0, Color.black), new Line(0.0, -150.0, 0.0, +150.0, Color.black), new Point(0.0, 0.0, Color.red), };

and see what your application displays. (You can copy out of the above and paste it into your Java IDE, or 'Save Link/Target as...' on this link.)

(Hint: To get the best view of this, resize your display so that it's square, rather than rectangular.)

It should display something interesting, and it should automatically display all of the above shapes in the window (no shapes, or parts thereof, should be outside of the display. The entire display should scale appropriately as you resize the window.  If all of these don't happen, you need to figure out what the problem is.

This page was last modified on 02 October, 2007