Question

I’m having trouble simulating a race between two competitors. This is your typical race program where you use a random number generator to determine what “moves” the competitors use. As seen in my code below, the track is composed of 50 rectangles, and the filled in rectangle shows the location of each competitor on the track. Some “moves” make the competitor jump 9 squares to the right, or 2 squares back, for example. When I run the applet, only the initial starting position is displayed; the applet doesn’t work. I realize it’s a lot of code, but what do I need to do to fix my problem? I’m really stuck at this point. Any help is appreciated. I have can only use AWT, not swing. This is an assignment for class :/ Here is the code:

import java.awt.*;
import java.applet.*;


    public class Example extends Applet
    {
        Image tortoise, hare;
        int tortX = 250, hareX = 250; 
        final int tortY = 100, hareY = 300, WIDTH = 15, HEIGHT = 50;
        int turn; String turnNum;
        int move; String tMove, hMove;

        public void init()
        {
            tortoise = getImage( getDocumentBase(), "images/tortoise.gif" );
            hare = getImage( getDocumentBase(), "images/hare.gif" );
            move = 0; turn = 0;
        }


        public void control()
        {
            while (( tortX < 985 ) || ( hareX < 985 ))
            {
                move = (int)(10 * Math.random());
                switch (move)
                {
                    case 1:
                    case 2:
                        tortX += (3 * WIDTH);
                        hareX += (9 * WIDTH);
                        tMove = "Fast Plod"; hMove = "Big Hop";
                        break;
                    case 3:
                    case 4:
                    case 5:
                        tortX += (3 * WIDTH);
                        hareX += WIDTH;
                        tMove = "Fast Plod"; hMove = "Small Hop";
                        break;
                    case 6:
                        tortX += WIDTH;
                        if (hareX == 250) {} // DO NOTHING
                        else if (hareX <= (250 + (11 * WIDTH)))
                            hareX = 250;
                        else 
                            hareX -= (12 * WIDTH);
                        tMove = "Slow Plod"; hMove = "Big Slip";
                        break;
                    case 7:
                    case 8:
                        tortX += (1 * WIDTH);
                        if (hareX == 250) {} // DO NOTHING
                        else if (hareX <= (250 + (WIDTH)))
                            hareX = 250;
                        else 
                            hareX -= (2 * WIDTH);
                        tMove = "Slow Plod"; hMove = "Small Slip";
                        break;
                    case 9:
                    case 10:
                        if (tortX == 250) {} // DO NOTHING
                        else if (tortX <= (250 + (5 * WIDTH)))
                            tortX = 250;
                        else 
                            tortX -= (6 * WIDTH);
                        tMove = "Slip"; hMove = "Fall Asleep. Zzz...";
                        break;
                        // Hare falls asleep. No action. 
                }

                turn++; turnNum = (turn + "");
                repaint();
                for (int i = 1; i <= 10; i++)
                {
                    delay();
                }
            }

            tortX = 985; hareX = 985;
            repaint();
        }

        public void paint( Graphics screen )
        {
            drawRace(screen);

            if (tortX >= 985)
            {
                screen.setFont(new Font("Times New Roman", Font.ITALIC, 48));
                screen.drawString("Tortoise Wins", 650, 240);
                clearCurrent(screen); 
                fillNext(screen);
            }
            else if (hareX >= 985)
            {
                screen.setFont(new Font("Times New Roman", Font.ITALIC, 48));
                screen.drawString("Tortoise Wins", 650, 240);
                clearCurrent(screen); 
                fillNext(screen);
            }
            else
            {       
                screen.drawString(("Turn " + turnNum), 621, 55);
                screen.setFont(new Font("Times New Roman", Font.ITALIC, 12));
                screen.drawString(tMove, 59, 65); screen.drawString(hMove, 66, 255); 
                clearCurrent(screen);
                fillNext(screen);
            }

            stop();
        }

        public void clearCurrent( Graphics s )
        {
            s.clearRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
            s.clearRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);

        }

        public void fillNext( Graphics s )
        {
            s.fillRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
            s.fillRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);

        }

        public void drawRace( Graphics s )
        {
            // GENERATES INITIAL GRAPHICS FOR RACE
            s.drawRect(250, 100, 750, 50);
            s.drawRect(250, 300, 750, 50);
            int lineX = 265, lineYi = 100, lineYf = 150;
            for (int i = 1; i <= 98; i++)
            {
                if (lineX == 1000)
                {
                    lineX = 265; lineYi = 300; lineYf = 350;
                }
                s.drawLine(lineX, lineYi, lineX, lineYf);
                lineX += 15;
            }
            s.fillRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
            s.fillRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);
            s.drawImage(tortoise, 59, 80, this);
            s.drawImage(hare, 66, 271, this);
            s.setFont(new Font("Times New Roman", Font.BOLD, 24));
            s.drawString("Race", 250, 55);
        }

        public void delay()
        {
            for (int i = 0; i < 90000000; i++)
            {
            }
        }

        public void stop()
        {
        }
    }

Answer 1

Your first problem is you actually never “start” the race…Sure your init the applet, but then, nothing…

Your second problem is the control method is block the Event Dispatching Thread, this means, they while you are in this method NOTHING will get painted to the screen. This is because the Event Dispatching Thread is also responsible for dispatching repaint requests.

You third problem is your violating the paint contact. You have a responsibility to call super.paint(screen) – paint is a complex method and should never ignore it unless you have a REALLY good reason do to so.

Your fourth problem is, you using an Applet instead of a JApplet. Better to ignore the AWT controls in favor of the Swing controls. Swing are more flexible and easier to extend.

Your fifth problem is you painting onto a top level container, this is never recommended. You are better using something like JPanel and overriding it’s paintComponent method (don’t forget to call super.paintComponent). Apart from everything else, it’s double buffered and will reducing flicking as the screen is updated.

Take a look at…

• Concurrency in Swing and How to use Swing Timer to solve you EDT blocking issues…
• Performing Custom Painting for ideas about painting in Swing