Boxball project - How do I write and use the onBallHittingBottom() method of the Boxball class? Study these two classes carefully.

1. Read and reread section 5.7 Making active objects affect other objects as you study this code.

       i. Figure 5.15 is the DropCollector class.  Compare the 
          DropCollector2 class (linked to below) to the 
          DropCollector class of page 156 of Williams textbook.
   
      ii. Figure 5.16 on page 157 is the FallingBall class.
          Compare to the FallingBall2 class shown below and
          linked to below.
   

2. I will make a link to the DropCollector2 class here later, so it opens up in a separate browser window, and closes automatically when you leave this page.

3. Ditto for the FallingBall2 class Java code. For now, you can look at the code here on this page.

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4. Java code for the DropCollector2 class.

   ---

   /* See pages 156-157 of the textbook (William's College manuscript)  10/09/2002 handout
                                                                        Wednesday's class
      Figure 5.15: Adding a collector to collect raindrops or falling balls.
    
                   How is DropCollector2 different from the book's DropCollector class?
   
                   How are the differences VERY HELPFUL for your Boxball assignment?
                                           ------------
   
                   How is THIS very helpful?  Do you see "this" in the code below?
                                                          ----
      Figure 5.16: Making a falling ball fill a collector
   
                   How is FallingBall2 different from the book's FallingBall class?
                   
                   How are the differences VERY HELPFUL and how do they apply to your
                   Boxball assignment?   
   */
   
   import objectdraw.*;
   import java.awt.*;
   import FallingBall2;
   
   public class DropCollector2 extends WindowController
   {
      private static final int  COLLECTOR_TOP = 295;  // Dry season before raindrops
      private static final int  SCREEN_WIDTH = 300; 
      private static final int  SCREEN_HEIGHT = 300;
   
      private static final int  CAPACITY_LEVEL = 50;
   
      private static final int  DROP_EFFECT = 12;      // How much it raises the water level
   
      private FilledRect collector;                   // The H O or water (lake)
                                                      //      2
      private int fontSize;
      private Text message0, message;
   
      private FilledRect capacityLevelLine;
   
      public void begin()
      {
         fontSize = 12;
   
         message0 = new Text("Start Sandbagging!", 10, 2, canvas);
         message0.hide();
   
         message = new Text("Click repeatedly to make falling raindrops...", 10, 16, canvas);
   
         collector = new FilledRect(0, COLLECTOR_TOP, SCREEN_WIDTH, SCREEN_HEIGHT, canvas);
         collector.setColor( Color.blue );
   
         capacityLevelLine = new FilledRect(0, CAPACITY_LEVEL, SCREEN_WIDTH, 1, canvas);  
         capacityLevelLine.setColor( Color.red );
      }
   
      public void onMouseRelease(Location point)   // Java's onMouseClick() has problems!  :-)
      {
         new FallingBall2(point, canvas, this);
      }
   
      public void onRaindropLanding( FallingBall2 drop )
      {
         if (collector.getY() > CAPACITY_LEVEL)
         {
            collector.setHeight( collector.getHeight() + DROP_EFFECT );
            collector.move(0, -DROP_EFFECT);
         }
         else
         {
            message0.show();
            message.setText("H 2 O overflow!  Water capacity reached!");
            message.setFontSize( ++fontSize );
         }
      }
   
      public double waterLevel()
      {
         return collector.getY();
      }
   
      public boolean fullOfWater()
      {
         return collector.getY() <= capacityLevelLine.getY();
      }
   }  
   
   

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5. Java code for the FallingBall2 class.

   ---

   // To be discussed on Wednesday, October 9th in class.
   
   // Compare to Figure 5.16: Making a falling ball fill a collector.
   // See page 157 of the Williams textbook (Chapter 5).
   
   /* Notice how "this" Java keyword is used below.
                  ----
   
      1. Why was it important to pass the ball back as a parameter to the
         onRainDropLanding() method? 
   
      2. Was it a mistake for the onRainDropLanding() method of the 
         DropCollector2 class to require a FallingBall2 object?  
   
      Hint:  Is it possible for raindrops or balls to be different sizes?
             Would a larger raindrop add more water to the collector
             than a smaller raindrop?
   */ 
   import java.awt.*;
   import objectdraw.*;
   import DropCollector2;
   
   public class FallingBall2 extends ActiveObject
   {
      private static final int BALLSIZE = 30;
   
      private DropCollector2 whereItIsRaining;
      private FilledOval ball;
   
   
      public FallingBall2(Location ballLocation, DrawingCanvas canvas, 
                          DropCollector2 theCollector)
      {
         whereItIsRaining = theCollector;
               
         ball = new FilledOval( ballLocation, BALLSIZE, BALLSIZE, canvas );
         ball.setColor( Color.magenta );
    
         start();     
      } 
   
      public void run()
      {
         while (( ball.getY() < whereItIsRaining.waterLevel() ) &&
                  !whereItIsRaining.fullOfWater() )
         {
            ball.move(0, 5);
            pause(50);
         }
         whereItIsRaining.onRaindropLanding( this );
         ball.hide();
      }
   }