Class 2 (8/28/02) Wednesday and Thursday JANUARY 16, 2003

Announcements:

• On Tuesday 01/21/03 (Day after Martin Luther King holiday), we will meet in the Wright 112 lab. Bring your account sheet with the user id and password. Your user id is the same as your UNI email user id. (Let me know ahead of time if you did not receive or do not know your user id or password for Wright Hall).

• Read over your lab and assignment #1 handout ahead of time. You will receive this in class on Tuesday, January 21st. It will be due by the START of class on Tuesday, January 28th. Familiarize yourself with this handout ahead of time by looking over the web page.

  Downloading the files for your first Java programming assignment. I will help you with this in the Wright 112 lab class.

  (Note: For those of you anxious to try out your jGrasp and Java at home, if you already installed it, go ahead and download the three files now. The Project .gpj file and the Java .java file are small, but the .jar file (objectdraw.jar) is bigger and take up about 2/3 of the space on a high density floppy diskette. It will take a bit longer to download. (Be sure to RIGHT-MOUSE CLICK on the links to the three files).

• Applications vs Applets - an applet example, with a hungry spider moving around on its web.
• Natural to want to work with graphics objects - shapes, text, lines, buttons, etc.
• The canvas. This applet canvas is 300 by 300. That means 300 rows of pixels by 300 columns of pixels.
• The coordinate system: it's upside down! As the Williams textbook explains, the top row of pixels is 0 and the bottom row of pixels is 299. The origin (0,0) is the top left corner of the applet window. The row numbers go from 0 to 299 instead of being numbered 1 to 300.

Graphics primitives - Williams College textbook objectdraw library

Basic entities we can draw are:

   
      FramedRect, FilledRect
      FramedOval, FilledOval
      Text
      Line

How we build these:

   new FramedRect(10, 10, 40, 60, canvas);

   new Line(x1, y1, x2, y2, canvas);

   new Text("hello there", x, y, canvas);

Demo 1. Rectangle and nested red square - uses both anonymous objects and a named objects.

Naming

OK, now say we want to write a program that has a red box. We need a name so that we can call methods associated with the object.

objectName.methodName( parameters );

Steps:

1) Declaration of object name - only save memory for a reference/pointer. No object created yet!!!

e.g., FilledRect box;

2) Constructs an object using "new"

e.g., box = new FilledRect (100, 200, 150, 150, canvas);

3) Call an object's methods using its name

box.setColor(Color.red);