Java "Crab" Applet

Hey all,

Am new here :wave:. 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 :rolleyes:.

The source code so far is...

Code:

---

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!

First Problem:

g.drawString(String, x, y);


Second:

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

Code:

---


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.

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.....

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....

Code:

---

// 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.

ok, have solved that problem now :afrog:.

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:

Code:

---

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?