CSC 121A Lab 3 - Spring 2005

Thursday, January 20, 2005
Due: Wednesday, January 26, 2005, 5:00PM

Answer all bulleted questions. Upload your answers and program files to the VikingWeb coursework section. Besides uploading your written answers to the VikingWeb, please turn in a printed copy either in class on the due date or leave a copy in the box outside my door later on during the day. (You may turn in the printed copies later than 5PM on the due date, but the files must be uploaded to VikingWeb at or before 5PM.)

Using Objects with Graphics

Most of the graphics programs we wrote in previous labs did not change behavior each time the program was executed. The exception was the last homework assignment which asked you to write a program that displayed shapes at random. The problem with that program was that each time the panel needed to be redrawn on the screen, the drawing changed. To create a more consistent drawing that remains the same each time it is drawn, we have to store information about the shapes and colors so that they can be reproduced in the same way each time the paintComponent method is called by the Java system.

To do this, let's design a set of classes to store information about the shapes we wish to draw. Objects of these classes will be "smart" enough to draw themselves given a Graphics object. Download and examine the following files and then run the TestDraw application to see how this program works:
[MyLine.java] [DrawPanel.java] [TestDraw.java]

Exercises (complete for homework)

• Extend the program above to randomly draw rectangles, ovals, and triangles. Create classes MyRectangle, MyOval, and MyTriangle. All of these classes should include x1, y1, x2, y2 coordinates, a color and a boolean flag to determine whether the shape is a filled shape. Declare constructors for each class with arguments for initializing all the fields (instance variables). Define draw methods for each class appropriately. To draw triangles, use the fillPolygon method of the Graphics class.

  Add arrays to the class DrawPanel for each shape type. The length of each array should be a random number between 1 and 5. The constructor of class DrawPanel should fill each of the arrays with shapes of random positions, size, and fill.
   

• Project Stage 1: Your first group project for this semester will involve writing an interactive drawing program. The program only needs to support a very simple user interface- it does not need to be very fancy. (However, once you get the basic functionality working you are welcome to use your imagination to improve the interface.)

  The first step of the project is to form groups of three or four people each. You should have your group identified by next Wednesday (January 26). Please email me the list of your group members by that date.

  Once you have identified your group, you should start looking over the project description (click here). There is not much on the page at this point but it will be updated over the next week.

Based on material from Deitel & Deitel, Java How to Program, 6e.

Last modified: Wed Jan 19 23:12:23 EST 2005