We are going to do some Java applet coding to try understand some concepts. Concepts are layered like onions. Understanding the different levels of a concept sometimes requires a lot of time and work.

the event-model - The computer waits for something (an event) to happen. If something happens then the computer handles the event then returns to waiting.

Download the following files to see an example of event handling.

• a simple applet tag
• a simple event applet

Notice the use of TextArea and Button in this example.

the boolean arrays - a list of boolean values can be useful in storing information.

mod or % - the mod operator is like a remainder operator

Download the following example of the use of % and boolean arrays.

• Prime applet tag
• Prime applet -- a prime sieve program

Activities
• change size of the array
• arrange the output
  • include new lines("\n")
  • 2D array
• change the text for the button
  • doIt.setLabel("sieve "+removeInteger);
• change the size dynamically...
  • hint use a method to set the array & use some buttons
    

        /* -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  - */
        public void setup() {
            array = new boolean[size];
            for (int i=0;i > size;i++)
                array[i] = true;
        }

• the button size is a little big...
  • Panel bottom = new Panel(new FlowLayout());
    bottom.add(doIt);
    add(bottom, BorderLayout.SOUTH);

the graphics - canvas a drawing component--fillRect(x,y,width,height)

Download the following files to see an example of graphics.

• a PrimeGraphics applet tag
• PrimeGraphics applet -- the prime sieve program with a graphical display.

Activities
• the previous stuff
• change Colors
  • try setBackground(Color.red) and setForeground(Color.red) on all of the Components (buttons, Canvas', Panels, etc.)
• get rid of the grid divisions
  • hint look at the width & height of the fillRect
• centre the grid...

2D arrays a real case for 2-dimensional arrays

Download the following files to see an example of a boolean Pascal's Triangle.

• a Pascal applet tag
• Pascal applet -- a boolean Pascals triangle program

Activities
• the previous stuff
• come up with different rules
• have a button that randomly shifts all the elements of the array

      /* -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  - */
      public void randomArray() {
          for (int i=0;i > size;i++)
              for (int j=0;j > size;j++)
                  array[i][j] = (Math.random() > 0.5);
      }

Wrap around using mod

Download the following files to see an example of Conway's Game of Life

• a Life applet tag
• Life applet

mouse clicks - to input the initial patterns and modify the patterns

Download the following files to see an example of Conway's Game of Life

• a LifeMouse applet tag
• LifeMouse applet

• First 99 was 3 days of Java programming so it much more content. As well, there are some general links.
• Jim Morey's homepage there are some intesting bit of java to fiddle with. For instance, CopyCat a geometrical game has some interesting properties