Exercise : Syntax errors

• The following program contains 12 mistakes! What are they? Once you think you've found them all, compile/run your corrected code.

  1 2 3 4 5 6 7 8 9 10 11 12 13 14

  import Java.*; public class PrettyPicture { public static void main(String[] args) { DrawingPanel panel = DrawingPanel(220, 150); setBackgroundColor(Color.YELLOW); Graphics g = panel.Graphics(); panel.setColor(new Color.BLUE); g.drawRectangle(50, 25); g.setColor("RED"); g.fillEllipse(130, 25, 42.1, 40.5); } }

answer on next slide...

Exercise - answer

1. line 1: incorrect import statement; should import java.awt.*
2. line 5: missing word new before 2nd occurrence of DrawingPanel
3. line 6: method name should be setBackground
4. line 6: missing panel. before setBackground
5. line 8: method name should be getGraphics
6. line 9: the setColor method is part of object g, not panel
7. line 9: should not write new before Color.BLUE
8. line 10: method name should be drawRect
9. line 10: missing two parameters from drawRect (width and height)
10. line 11: color should be specified as Color.RED, not "RED"
11. line 12: method name should be fillOval
12. line 12: wrong parameter types; width/height must be integers

Exercise - corrected version

• Here is a corrected version of the program:

  import java.awt.*;
  
  public class PrettyPicture {
      public static void main(String[] args) {
          DrawingPanel panel = new DrawingPanel(220, 150);
          panel.setBackground(Color.YELLOW);
          
          Graphics g = panel.getGraphics();
          g.setColor(Color.BLUE);
          g.drawRect(50, 25, 10, 10);
          g.setColor(Color.RED);
          g.fillOval(130, 25, 42, 40);
      }
  }