Notes on Assignment 3

Here are some sample files. More notes are forthcoming.

• Circle.java
• CircleTester.java
• circletester.html
• Square.java
• SquareTester.java
• squaretester.html
• DrawingAssistant.java
• SimplePicture.java
• simplepicture.html

Common Problems

A number of you neglected to center your circles and squares on the given point. Once you realized that you were supposed to center it, most of you then figured out how to do so. (If you lost points because of this, mail me the new method and I'll update your grade.)

A few of you decided that everything should extend Applet. However, there should only have been one applet in your suite of classes. If you did extend Applet, it is likely that you found it difficult to write getSize.

What else? I'm still seeing some problems with comments and indentation. I'm likely to get fairly nasty on the next assignment. (Now that you've used Javadoc, you understand some of my conventions.)

Bounds

Some of you wanted to get the bounds of the graphics area, but couldn't figure out a way to do so. If you carefully read the documentation, you will find that you might be able to do the following.

• First, get the clipping rectangle of the graphics object.

      Rectangle clip = g.getClipBounds();
  

• Next, extract the left, right, width and height from that.

      int leftBorder = clip.x;
      int topBorder = clip.y;
      int width = clip.width;
      int height = clip.height;
  

• Finally, we can generate interesting centers.

      int x = leftBorder + (Math.abs(generator.nextInt()) % width);
      int y = topBorder + (Math.abs(generator.nextInt()) % width);
  

You may want to think if I got everything right (particularly the last step).

Testing

As you have hopefully noted from the reading, component testing is quite important. Hence, two two basic components (Circle and Square) have individual testers. There is not a tester for DrawingAssistant because the SimplePicture applet does the testing.

Note that you should be fairly careful in your testing and analysis. If there are two different constructors, check to see what each one does. If there is a chance that a method affects its arguments, check afterwards.

Outlining Your Circles

As an example of the kind of thing you might have done for some extra credit, I've created a NewCircle class that outlines the circle in the ``complement'' of the circle's main color.

• NewCircle.java
• NewCircleTester.java
• newcircletester.html

Fun With Randomness

• Pixelation.java
• pixelation.html

This is just an example of fun with the random drawing mechanism. It illustrates some of the problems with that mechanism. (Try covering up parts of the picture.) You can run it with

/home/rebelsky/bin/pixelation

An Alternate Design

We can simplify the design of the program by using inheritance. We'll discuss this in class.

History

• Created Tuesday, February 16, 1999.
• Updated Wednesday, February 17, 1999 (added notes on clip rects and some other stuff).