Java "Crab" Applet

[robcyb]

Hey all,

Am new here . Nice to see fellow developers helping one another.

I have recently began to delve into looking at Java Applets and animation of objects within applets. As a mini-project I have embarked on creating a "crab" Applet that simulates some sort of crab behaviour.

Each instance of a "crab" is to move around randomly on the screen (within the limits of the applet window) and when a collision is detected the coordinates are inverted to creat a "bounce" effect. However, the work I have done so far is very simple and does not necessarily do much to what I would like to achieve from this little adventure .

The source code so far is...

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

class CollideCrab
{
        int width, height;
        public static final int diameter=20;
        double x, y, xinc, yinc, coll_x, coll_y;
        boolean collide;
        Color color;
        Graphics g;
        
        public CollideCrab(int w, int h, int x, int y, double xinc, double yinc, Color c)
        {
                width=w;
                height=h;
                this.x=x;
                this.y=y;
                this.xinc=xinc;
                this.yinc=yinc;
                color=c;
        }

        public double getCenterX() {return x+diameter/2;}
        public double getCenterY() {return y+diameter/2;}

        public void move()
        {
                if (collide)
                {
                        double xvect=coll_x-getCenterX();
                        double yvect=coll_y-getCenterY();

                        if((xinc>0 && xvect>0) || (xinc<0 && xvect<0))
                                xinc=-xinc;

                        if((yinc>0 && yvect>0) || (yinc<0 && yvect<0))
                                yinc=-yinc;

                        collide=false;
                }

                x+=xinc;
                y+=yinc;

                if(x<0 || x>width-diameter)
                {
                    xinc=-xinc;
                    x+=xinc;
                }

                if(y<0 || y>height-diameter)
                {
                    yinc=-yinc;
                    y+=yinc;
                }
        }

        public void hit(CollideCrab b)
        {
                if(!collide)
                {
                        coll_x=b.getCenterX();
                        coll_y=b.getCenterY();
                        collide=true;
                }
        }

        public void paint(Graphics gr)
        {
                g=gr;
                g.setColor(color);
                g.fillOval((int)x,(int)y,diameter,diameter);
        }
}

public class fiddlerCrabs extends Applet implements Runnable
{
        Thread runner;
        Image Buffer;
        Graphics gBuffer;
        CollideCrab crab[];

        static final int MAX=5;

        public void init()
        {
                Buffer=createImage(size().width,size().height);
                gBuffer=Buffer.getGraphics();

                crab=new CollideCrab[MAX];

                int w=size().width;
                int h=size().height;

                crab[0]=new CollideCrab(w,h,50,20,1.5,2.0,Color.orange);
                crab[1]=new CollideCrab(w,h,60,100,2.0,-3.0,Color.red);
                crab[2]=new CollideCrab(w,h,15,70,-2.0,-2.5,Color.pink);
                crab[3]=new CollideCrab(w,h,150,60,-2.7,-2.0,Color.cyan);
                crab[4]=new CollideCrab(w,h,210,30,2.2,-3.5,Color.magenta);
        }

        public void start()
        {
                if (runner == null)
                {
                        runner = new Thread (this);
                        runner.start();
                }
        }

        public void stop()
        {
                if (runner != null)
                {
                        runner.stop();
                        runner = null;
                }
        }

        public void run()
        {
                while(true)
                {
                        try {Thread.currentThread().sleep(30);}
                        catch (Exception e) { }

                        for(int i=0;i<MAX;i++)
                                crab[i].move();

                        handleCollision();

                        repaint();
                }
        }

        boolean collide(CollideCrab b1, CollideCrab b2)
        {
                double wx=b1.getCenterX()-b2.getCenterX();
                double wy=b1.getCenterY()-b2.getCenterY();

                double distance=Math.sqrt(wx*wx+wy*wy);

                if(distance<b1.diameter)
                {
                        return true;
                }

                        return false;
        }


        private void handleCollision()
        {
                for(int i=0;i<MAX;i++)
                        for(int j=0;j<MAX;j++)
                                {
                                        if(i!=j)
                                        {
                                                if(collide(crab[i], crab[j]))
                                                {
                                                        crab[i].hit(crab[j]);
                                                        crab[j].hit(crab[i]);
                                                }
                                        }
                                }
        }

        public void update(Graphics g)
        {
                paint(g);
          }

          public void paint(Graphics g)
        {
                gBuffer.setColor(Color.blue);
                gBuffer.fillRect(0,0,size().width,size().height);

                for(int i=0;i<MAX;i++)
                                crab[i].paint(gBuffer);

                g.drawImage (Buffer,0,0, this);
          }
}

As you can see from the code, it's very simple. I would like help on the following issues though .

I would like the crabs to each have a label above them (crabx) to keep a track of what each crab is.

A for loop for creating an instance of each crab with the random startx and starty variables to move a crab across the scene. (so that more crabs can be added dynamically and not have to hard code each crab).

If anyone could help, it would be most appreciated!

[System_Error]

First Problem:

g.drawString(String, x, y);


Second:

Create two random objects (possibly just one) and an array of crab objects:

Crab[] c = new Crab[5];
for (int index=0; index<c.length; ++c)
{
   c = new Crab(randomx.nextInt(), randomy.nextInt());
}

That's not everything, but it should get you started.

[robcyb]

Thanks for the help and advice!

Have now done the modficications and a major code cleanup/variable naming changes.

However, the problem I have now is with the starting position of each crab (they all seem to start at the same point??). It's probably my poor lack of math logic.

New Code.....

// fiddlerCrabs.java
// Robert Simmons 13th Feburary 2006.
// Last Change: 15th February 2006 @ 11:56.

import java.applet.*;
import javax.swing.*;
import java.util.*;
import java.awt.*;
import java.awt.Graphics.*;

public class fiddlerCrabs extends JApplet implements Runnable
{
    Thread tThread;
    Image tImageBuffer;
    Graphics tGraphicsBuffer;
    Crab tCrab[];

    // Number of crabs to be drawn to scence.
    static final int tNoOfCrabs = 10;

    public void init()
    {
        tImageBuffer = createImage(size().width,size().height);
        tGraphicsBuffer = tImageBuffer.getGraphics();

        tCrab = new Crab[tNoOfCrabs];

        int tWidth = size().width;
        int tHeight = size().height;

        for (int i=0; i < tCrab.length; i++)
        {
            String tCrabLabel = ("Crab" + (i+1));

            int tPositionX = ((int)Math.random() + (50)*2);
            int tPositionY = ((int)Math.random() *3 + 20);
            double tIncrementX = (double)Math.random() + 1.5;
            double tIncrementY = (double)Math.random() + 2.0;

            // Create new instance of crab, passing: width, height, position on X Axis, position on Y Axis, Increment on X Axis, Increment on Y Axis, Colour and Text Label.
            tCrab[i] = new Crab(tWidth, tHeight, tPositionX, tPositionY, tIncrementX, tIncrementY, Color.black, tCrabLabel);
        }
    }

    public void start()
    {
        if (tThread == null)
        {
            tThread = new Thread (this);
            tThread.start();
        }
    }

    public void stop()
    {
        if (tThread != null)
        {
            tThread.stop();
            tThread = null;
        }
    }

    public void run()
    {
        while(true)
        {
            try
            {
                Thread.currentThread().sleep(30);
            }

            catch (Exception e)
            {
                // Do Nothing.
            }

            for(int i=0;i<tNoOfCrabs;i++)
            {
                tCrab[i].move();
            }

            handleCollision();

            repaint();
        }
    }

    boolean collide(Crab pCrab1, Crab pCrab2)
    {
        double wx = pCrab1.getCenterX() - pCrab2.getCenterX();
        double wy = pCrab1.getCenterY() - pCrab2.getCenterY();

        double distance = Math.sqrt(wx*wx+wy*wy);

        if(distance < pCrab1.tCrabDiameter)
        {
            return true;
        }

        return false;
    }


    private void handleCollision()
    {
        for(int i=0; i < tNoOfCrabs; i++)
        for(int j=0; j < tNoOfCrabs; j++)
        {
            if(i!=j)
            {
                if(collide(tCrab[i], tCrab[j]))
                {
                    tCrab[i].hit(tCrab[j]);
                    tCrab[j].hit(tCrab[i]);
                }
            }
        }
    }

    public void update(Graphics g)
    {
        paint(g);
    }

    public void paint(Graphics g)
    {
        tGraphicsBuffer.setColor(Color.gray);
        tGraphicsBuffer.fillRect(0,0,size().width,size().height);

        for(int i=0;i<tNoOfCrabs;i++)
        {
            tCrab[i].paint(tGraphicsBuffer);
        }

        g.drawImage (tImageBuffer,0,0, this);
    }
}

And the class File....

// Crab.java
// Class File for constructing an instance of crab.
// Robert Simmons 13th Feburary 2006.
// Last Change: 15th February 2006 @ 11:56.

import java.awt.*;
import java.awt.Graphics.*;

class Crab
{
    int tCrabWidth, tCrabHeight;

    // Crab Circle Diameter.
    public static final int tCrabDiameter = 15;

    double tPositionX, tPositionY, tIncrementX, tIncrementY, tCollisionX, tCollisionY;
    boolean tCollisionDetected;
    String tCrabLabel;
    Color tColour;

    public Crab(int pCrabWidth, int pCrabHeight, int pCrabPositionX, int pCrabPositionY, double pIncrementX, double pIncrementY, Color pColour, String pString)
    {
        tCrabWidth = pCrabWidth;
        tCrabHeight = pCrabHeight;
        this.tPositionX = pCrabPositionX;
        this.tPositionY = pCrabPositionY;
        this.tIncrementX = pIncrementX;
        this.tIncrementY = pIncrementY;
        tColour = pColour;
        tCrabLabel = pString;
    }

    public double getCenterX()
    {
        return tPositionX + tCrabDiameter / 2;
    }

    public double getCenterY()
    {
        return tPositionY + tCrabDiameter / 2;
    }

    public void move()
    {
        if (tCollisionDetected)
        {
            double tVectorX = tCollisionX - getCenterX();
            double tVectorY = tCollisionY - getCenterY();

            if((tIncrementX > 0 && tVectorX > 0) || (tIncrementX < 0 && tVectorX < 0))
            {
                tIncrementX =- tIncrementX;
            }

            if((tIncrementY > 0 && tVectorY > 0) || (tIncrementY < 0 && tVectorY < 0))
            {
                tIncrementY =- tIncrementY;
            }

            tCollisionDetected = false;
        }

        tPositionX += tIncrementX;
        tPositionY += tIncrementY;

        if(tPositionX < 0 || tPositionX > tCrabWidth - tCrabDiameter)
        {
            tIncrementX =- tIncrementX;
            tPositionX += tIncrementX;
        }

        if(tPositionY < 0 || tPositionY > tCrabHeight - tCrabDiameter)
        {
            tIncrementY =- tIncrementY;
            tPositionY += tIncrementY;
        }
    }

    public void hit(Crab pCrab)
    {
        if(!tCollisionDetected)
        {
            tCollisionX = pCrab.getCenterX();
            tCollisionY = pCrab.getCenterY();
            tCollisionDetected = true;
        }
    }

    public void paint(Graphics pGraphics)
    {
        pGraphics.setColor(tColour);
        pGraphics.fillOval((int)tPositionX,(int)tPositionY,tCrabDiameter,tCrabDiameter);
        pGraphics.drawString(tCrabLabel,((int)tPositionX)-7,((int)tPositionY)-5);
    }
}

If anyone could help, it would be greatly appreciated.

[robcyb]

ok, have solved that problem now .

[robcyb]

Ok, once again I have stumbled across yet another problem.

I am trying to add a layout manager to add some simple GUI functionality. However whatever I setup, it's getting overriden by the painting of the background and the button is getting lost.

I have done the following:

Container tContent = getContentPane();
        
        JButton tStart = new JButton("Start");
        tContent.add(tStart, BorderLayout.NORTH);
        setContentPane(tContent);
        setLayout(new FlowLayout());
        
        setVisible(true);

However, I want to be able to add the rest to the south of the borderlayout (the crabs being drawn).

How do I go about setting this up :S?