CSSE 220: Object-Oriented Software Development
Introduction to Java Graphics — CircleOfCircles

Work on this exercise by yourself, but be quick to ask questions of your instructor, student assistants and classmates as desired.

Getting started

1. Unzip this IntroToJavaGraphics1.zip file, putting it into your JavaProjects folder.
2. In Eclipse, choose File ~ Import. In the dialog box that opens:

   1. Choose Existing Projects Into Workspace under the General category. Press Next.
   2. Browse to find the IntroToJavaGraphics1 folder in your JavaProjects folder.
   3. Press Finish.

3. Add your project to your individual repository for this course.
4. With your instructor, browse the code and draw a UML class diagram for the project. Note especially:

   • How Main:

     • Constructs a SimpleFrame but does not need a variable for the object

   • How SimpleFrame:

     • Sets its size and other characteristics
     • Uses an Asker to get a width and color from the user
     • Adds SquarePanels

   • How Asker:

     • Displays a message dialog
     • Gets and parses information from the user
     • Constructs a Color object
     • Uses getters to allow others to get information from it

   • How SquarePanel:

     • Sets its preferred size and background
     • Calls its superclass' paintComponent method in its paintComponent method
     • Sets a color for drawing
     • Draws a square with the size and color specified when the SquarePanel was constructed
     • Do you see why SquarePanel needs fields for the square's width and color?
   • When you run the program, note:

     • The graphics coordinates system: (0, 0) is the upper-LEFT corner of a panel and the y-axis goes DOWN (not up) as y increases.
     • How resizing the frame causes the two panels to “flow” in the frame.

5. In the paintComponent method of SquarePanel, do the TODO, adding commands that use the Graphics object to draw the things specified by the TODO.
6. Commit your project to your repository when you are done.

CircleOfCircles

1. In Eclipse, create a new Java project called CircleOfCircles

2. Add your project to your individual repository for this course.
3. Add to the class four classes, with functionality as follows (and using IntroToJavaGraphics1 as your example):

   • Main: just constructs the frame.
   • Asker: asks the user for a big radius, small radius and number of circles, and provides getters to get each of these three integers.
   • CircleFrame: a JFrame that uses Asker to get two sets of numbers (big radius, small radius and number of circles) and then adds three CirclePanes:
     • The first CirclePanel is one background color (whatever color you wish) and should have big radius 100, small radii 20, and 10 circles.
     • The second CirclePanel is another background color and should have big radius, small radii and number of circles as specified by the user.
     • The third CirclePanel is yet another background color and should also have big radius, small radii and number of circles as specified by the user.

   • CirclePanel: a JPanel whose sole constructor accepts a background color and a triple of numbers (big radius, small radius and number of circles) and displays a “circle of circles” based on those numbers, per these examples:

     

     The three panels were generated by the following numbers:

     • Pink panel: big, imaginary circle has radius 100; each small circle has radius 20; there are 10 circles.
     • Cyan panel: big, imaginary circle has radius 200; each small circle has radius 100; there are 50 circles.
     • Yellow panel: big, imaginary circle has radius 100; each small circle has radius 50; there are 200 circles.

   A few hints:

   • Work incrementally. For example, implement and test each of these stages, one by one:
     • Stage 1: Make a frame appear.
     • Stage 2: Make a colored panel show up on the frame.
     • Stage 3: Make a single circle appear on the panel.
     • Stage 4: Make the circle of circles in the first CirclePanel (with big radius 100, small radii 20, and 10 circles).
     • Stage 5: Get user input and all make each of the three CirclePanels appear with its correct circle of circles.
   • To loop through a circle of things:
     • Let your loop variable be the angle, starting it at 0 and going in appropriate increments to 2 * Math.PI
     • For an angle of θ, the point on the circle is (r cos(θ), r sin(θ)).
     • Don't forget to deal with the graphics system — points with negative coordinates won't show up!
   • You cast an expression BLAH to the int type by using the notation:

         (int) (BLAH)
     

4. Commit your project to your repository when you are done (and at intermediate points if you wish). Be sure that every class:
   • Has correct and complete documentation.
   • Obeys our code conventions (use Control-Shift-F).