Lab 2 Wrap-Up, Methods Exercise

Tom Kelliher, CS 116

Sept. 20, 2000

Administrivia

Announcements

1. Friday's quiz covers Chapter 2.

2. Lab 2 due Friday.

3. Postlab programming exercises due Monday, Sept. 25. Hand-in hardcopy.

4. Third programming exercise available. ``Alphabetical ordering'' not important. Uniqueness is.

Assignment

Read 3.1--2.

From Last Time

Lab 2.

Outline

1. Lab 2 wrap-up: comments, discussion.

2. Methods Exercise: shaded ball method.

Coming Up

Introduction to widgets.

Lab 2 Wrap-Up

1. Setting colors in drawHole():

   private void drawHole(int n, Graphics g)
   {
      int X0 = 50,   // x-anchor
      Y0 = 50,       // y-anchor
      W0 = 350,      // initial width
      H0 = 200,      // initial height
      X_INC = 30,    // x-anchor increment
      Y_INC = 10,    // y-anchor increment
      RG_INC = 10,   // red-green increment
      BLUE_INC = 25; // blue increment
   
      g.setColor(new Color(n * RG_INC,
                           n * RG_INC,
                           (n + 1) * BLUE_INC));
   
      g.fillOval(X0 + n * X_INC, Y0 + n * Y_INC,
                 W0 - n * X_INC, H0 - n * 2 * Y_INC);
   }
   

   1. Restrictions on the arguments passed to the Color constructor.

   2. ``My text won't display'' problems.

   3. Customizing the shading pattern.

   4. Declaring and using variables.

      Remember: the computer knows nothing. It cannot figure out what you want to occur. You must instruct it, step by step.

2. The programming exercise: See the java.awt.Graphics class description in Section 2.8.

3. Dealing with a blank applet. If you see this error message at the bottom of AppletViewer:

   Start: applet not initialized
   

   Exit AppletViewer and in JWS do the following: Open the Project menu, choose Properties, and look at the Run tab. Check that the Main Class Name entry matches your class name, including capitalization.

Method design Exercise

Working in your lab groups, design a Java Method to produce a shaded ball like this:

Use the following signature for your method:

void drawBall(Graphics g, int x, int y, int radius)