Creating Java applet

[maja neskovic]

I have to create a Java applet, but I don't know how. It should display a simulation a running rabbit in 10 circles, explaining the For cycle in a programming language C. I tried to make it in NetBeans, but I couldn't. Can anubody please help me? Any hint, useful site or line of code... I would be very, very grateful

[maja neskovic]

This code is all I have:

package org.me.hello;
import java.applet.Applet;
import java.awt.*;
import java.awt.Font;
import java.awt.event.*;
public class NewApplet extends Applet implements Runnable {
  int frameNumber = 0;
  int delay = 100;
  Thread animatorThread;
  boolean frozen = false;
     Color redColor;
    Color bgColor;
    Font f = new Font("TimesRoman", Font.BOLD, 20);
    public void init() {
    String str;
    addMouseListener(new MouseAdapter() {
      public void mousePressed(MouseEvent e) {
        if (frozen) {
          frozen = false;
          start();
        } else {
          frozen = true;
          stop();
        }
      }
    });
  }
  public void start() {
    if (!frozen) {
      if (animatorThread == null) {
        animatorThread = new Thread(this);
      }
      animatorThread.start();
    }
  }
  public void stop() {
    animatorThread = null;
  }
  public void run() {
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
    long startTime = System.currentTimeMillis();
    Thread currentThread = Thread.currentThread();
    while (currentThread == animatorThread) {
      frameNumber++;
      repaint();
      try {
        startTime += delay;
        Thread.sleep(1000);
      } catch (InterruptedException e) {
        break;
      }
    }
  }
  public void paint(Graphics g) {
    g.setFont(f);
    g.setColor(Color.red);
    g.drawString("FOR petlja", 120, 20);
    g.setColor(Color.black);
    setBackground( Color.white );
    g.drawOval(60, 60, 220, 140 );
    g.drawOval( 80, 80, 180, 100);
    g.drawString("Krug broj " + frameNumber, 20, 50);
    setBackground (Color.white);
    g.setColor (Color.blue);
    Dimension d = getSize();
    if (frameNumber % 2 == 1) {
      // On odd frames, draw the ball at the top.
      g.fillOval (70, 0, 20, 20);
    }
    else {
      g.fillOval (70, 90, 20, 20);
    }
  }
}

It should be made into a rabbit (instead of ball) which will ran on the drawn path and counter will count his circuits to simulate For loop. Can anybody help, please...?

[Ulf Dittmer]

What ideas have you had? What do you think needs to be changed, and how?

[maja neskovic]

I have to put a picture of rabbit instead of this ball, and the rabbit should be running around the track simulating running in circle and making loop. The counter should count those circles. Do you have any idea how to do it? As you can see, I'm new in Java programming and I really don't know how to do it, but I have to make this... I would be very grateful

[Ulf Dittmer]

If you have the rabbit as an image, then you can use Graphics.drawImage to draw it. You can obtain an Image object through various means, the easiest probably being AppletContext.getImage.

You'll have to find a way to keep track of where the rabbit should be (maybe divide its path around the circle in 100 steps), and then figure out how to get from numbers 0..100 to (X,Y) positions around the circle.

Once you've counted up to 100 (meaning the rabbit has been around the circle), increment the counter and display it using Graphics.drawString.

[maja neskovic]

I found an image. Do you think it's ok? Can you please explain me in more detail how to do the rest?

[Ulf Dittmer]

I found an image. Do you think it's ok?

Um, if you don't know that, how can we? It's your project, after all... It won't be animated once it's drawn on a Graphics object, though.

Can you please explain me in more detail how to do the rest?

This sounds like an assignment that you should be working on in order to learn something, so we don't want to rob you of the opportunity to do so by giving away too much. I'd break this down in smaller steps, maybe start with writing an applet that loads an image and display it at arbitrary screen locations. The CodeBarn has an example applet that does something like that. Then you could write math functions that provide you with (X,Y) coordinates along a circle.

[maja neskovic]

My professor gave me this assignment because I am a good student, but he knows that I'm not familiar with Java. The simulation doesn't have to be complicated. He needs this for showing students in simulating For loop in programming language C and he actually made me to do this. That's why I need help with this

I found the displayed image on the Internet, I have only it's URL. Can it be imported in applet that is created in NetBeans? I have looked at this site, but I don't understand this:

1. Create an instance of Image
2. Create an instance of MediaTracker
3. Add the Image to the MediaTracker instance
4. Call the MediaTracker object's waitForAll() method. The method will block until the image is fully downloaded.
5. Override the applet's paint() method, and add a method call to drawImage().

It's so complicated... I hope I didn't confused you too and THANK YOU very much

Best regards!

[Ulf Dittmer]

The steps 1 through 5 are what that applet does; it's very short, so it shouldn't be hard to correlate those steps with the lines of code that carry out those steps. Reading the javadocs of the involved methods and classes will also help.

It makes no difference to the working of the applet if you create it using some IDE or in a text editor. In order for an applet to load images, those images will need to be located in your server, though, along with the applet class files.

Have you worked with applets before, so that you know their lifecycle, how to deploy them, and which methods do what? If not, start here: http://java.sun.com/docs/books/tutorial/deployment/applet/

[maja neskovic]

I have read this tutorial, but I didn't understand all. My code doesn't have separately defined classes, everything is in the applet I put the picture in the folder with applet, but I get confused in writing code for image importing. It probably was a mistake...? I have no idea how to make something looking like wanted simulation. I haven't worked with applets nor with Java so far, I have only read in tutorials about applets. Thank you for caring about my problem

[Ulf Dittmer]

If you haven't worked with Java so far, I'd suggest to get an introductory book for getting started. You could also work through the Sun Java Tutorial (http://java.sun.com/docs/books/tutorial/), particularly the section Getting Started and Learning the Java Language (and possibly Essential Java Classes) before you start working on applets.

[maja neskovic]

Thank you I'm already reading about Java, but I have to make applet in parallel because it has to be made until Monday.

[maja neskovic]

I have written this code:

package org.me.pack;
import java.applet.Applet;
import java.awt.*;
import java.net.*;
public class MyApplet extends Applet {
Font bigFont;
Color blueColor;
Color grayColor;
Color whiteColor;
Image rabbit;
URL base;
MediaTracker mt;
public void init() {
mt= new MediaTracker(this);
bigFont=new Font("Arial", Font.BOLD,20);
blueColor=Color.BLUE;
grayColor=Color.GRAY;
whiteColor=Color.WHITE;
try {
base=getDocumentBase();
}
catch (Exception e) {}
rabbit=getImage(base, "White_Rabbit1.gif");
mt.addImage(rabbit, 1);
try {
mt.waitForAll();
}
catch (InterruptedException e) {}
}
public void paint(Graphics g) {
g.setFont(bigFont);
g.setColor(blueColor);
g.drawString("FOR petlja",230,20);
g.setColor(grayColor);
g.drawOval(40, 100, 450, 300);
g.drawOval(70, 130, 390, 240);
g.fillOval(40, 100, 450, 300);
g.setColor(whiteColor);
g.fillOval(70, 130, 390, 240);
g.drawImage(rabbit, 40, 140, 60, 60, this);
}
}

It displays the image, but I don't know how to make image move. It should be rounding in a circle. Please, help me, I'm desperate

[Ulf Dittmer]

Please edit your post to UseCodeTags. It's unnecessarily hard to read the code as it is, making it less likely that people will bother to do so.

Earlier I wrote this:

You'll have to find a way to keep track of where the rabbit should be (maybe divide its path around the circle in 100 steps), and then figure out how to get from numbers 0..100 to (X,Y) positions around the circle.

That seems like a good next step, since currently the image is drawn at a fixed location.

[maja neskovic]

Ok, here is the code:

  
package org.me.pack;
import java.applet.Applet;
import java.awt.*;
import java.net.*;
public class MyApplet extends Applet {
Font bigFont;
Color blueColor;
Color grayColor;
Color whiteColor;
Image rabbit;
URL base;
MediaTracker mt;
public void init() {
mt= new MediaTracker(this);
bigFont=new Font("Arial", Font.BOLD,20);
blueColor=Color.BLUE;
grayColor=Color.GRAY;
whiteColor=Color.WHITE;
try {
base=getDocumentBase();
}
catch (Exception e) {}
rabbit=getImage(base, "White_Rabbit1.gif");
mt.addImage(rabbit, 1);
try {
mt.waitForAll();
}
catch (InterruptedException e) {}
}
public void paint(Graphics g) {
g.setFont(bigFont);
g.setColor(blueColor);
g.drawString("FOR petlja",230,20);
g.setColor(grayColor);
g.drawOval(40, 100, 450, 300);
g.drawOval(70, 130, 390, 240);
g.fillOval(40, 100, 450, 300);
g.setColor(whiteColor);
g.fillOval(70, 130, 390, 240);
g.drawImage(rabbit, 40, 140, 60, 60, this);
}
}   

Do you have any idea how to do that circle divide and image moving in those little steps?

[Ulf Dittmer]

Do you really not indent your code?

[maja neskovic]

Well, no

[Ulf Dittmer]

Do you have any idea how to do that circle divide and image moving in those little steps?

Let's say you have a variable "t" which runs from 0 to 100. Both 0 and 100 would represent the image being displayed at the top of the circle (at 12 o'clock), while 50 would mean to display the image at the bottom of the circle (at 6 o'clock), 25 means 3 o'clock, and 75 means 9 o'clock.

Now you need two functions that calculate x and y as a function of t, respectively. As a hint, both functions will have the diameter (or radius) of the circle in them, one of them will involve a cosine function, and the other will involve a sine function.

Does this help?

[maja neskovic]

I understand, but I how and where to implement these functions? Do you mean something like writing for loop that goes from 0 to 99 which will call functions?

[Ulf Dittmer]

Yes, you need to write a loop, and in each iteration the image will be drawn in a slightly different place from the previous iteration.

[maja neskovic]

Thanks I'll try.

I have one more question: can I make simulation with buttons in simple Java applet or I need JApplet, or something else?

Greetings!

[Ulf Dittmer]

You can use either. Applet is for applets that use the AWT toolkit, while JApplet is for applets that use the Swing toolkit.

The code above is AWT, so if you're basing your efforts on that, then you should stick with Applet.

[maja neskovic]

And what about JPanel and JApplet?

[Ulf Dittmer]

What about them?

[maja neskovic]

What is the difference between them? Should I use them?

[Ulf Dittmer]

You should use JPanel and JApplet if you intend to use Swing; you should Panel and Applet of you intend to use AWT. If you're not sure what the difference between AWT and Swing is -and I suspect that you don't, since you're new to Java- you might as well stick with AWT, since the code you posted uses that. There's no sense in complicating the task at hand by switching to a different API.

[maja neskovic]

Thank you for explanation. I have to make buttons also on my applet... Can it be done using only AWT?

[Ulf Dittmer]

Sure you can. I suggest to inspect the classes of the java.awt package to see what's available. You'll also find various AWT tutorials online.

[maja neskovic]

Thank you very much. I hope I can ask you again if I have problems... Greetings!

[maja neskovic]

Hello! I have written some code, but I did't know how to make image move, I mean I don't know how to write that For loop and how to include these defined threads... Here's the code:

  
import java.applet.Applet;
import java.awt.*;
import java.net.*;
import java.awt.Graphics2D;
public class moj extends Applet implements Runnable{
    int width;
    int height;
    Image rabbit;
    URL base;
    MediaTracker mt;
    Thread anim;
 public void run() {
     Thread trenutni = Thread.currentThread();
     while(anim == trenutni) {
         repaint();
         try {
             Thread.sleep(100);
             } catch (InterruptedException e) {}
     }
 }
 public void update(Graphics screen) {
     paint(screen);
 }
    public void init() {

        width = getSize().width;
        height = getSize().height;
        setBackground(new Color(60,179,113 ));
        mt = new MediaTracker (this);
        try {
               base = getDocumentBase();
         }
        catch (Exception e) {}
        rabbit = getImage(base, "White_Rabbit1.gif");
                  mt.addImage(rabbit,1);
                    try {
               mt.waitForAll();
          }
        catch (InterruptedException  e) {}
              Button button = new Button("Start");
        add(button);
        Button button1 = new Button("Stop");
        add(button1);
    }
public void start() {
    if(anim==null){
        anim = new Thread(this);
        anim.start();
    }
}
public void stop(){
    if (anim != null){
        anim = null;
    }
}
    public void paint(Graphics g) {
        g.setColor(new Color(105,105,105));
        g.fillArc(100, 100, 550, 450, 0, 360);
        g.setColor(new Color(60,179,113 ));
        g.fillArc(150, 150, 450, 350, 0, 360);
        g.drawImage(rabbit, 100, 325, this);
        g.setColor(new Color(0,100,0));
        g.fillOval(30,30,20,20);
        g.fillOval(40,40,20,20);
        g.fillOval(30,50,20,20);
        g.fillOval(20,40,20,20);

       }
    }
  

Image is also flickering... I have written the update method and it doesn't stop flickering. Can you help please with all these problems?

[Ulf Dittmer]

I did't know how to make image move

The code passes fixed value to the drawImage method, so there's no way it can move, but I'm sure you know that. You need to program a loop that provides x and y coordinates in a circle, like I mentioned before; how far have you come with that?

If you want to avoid flickering, check out a technique called "double buffering"; searching for "awt double buffering" will find relevant pages. I'd leave that for last, once everything else is working.

[maja neskovic]

That is the thing I don't know - how to program coordinates in circle (or ellipsis) and how to make image moving, but not drawing on any point of that programmed circle...? Can you explain me that more detail, please?

[Ulf Dittmer]

Here's a hint: If you want to draw a circle of radius RAD that is centered on the point (X0, Y0), then the following equation holds for all points (x, y) on the circle's circumference:

(x - X0) ^ 2 + (y - Y0) ^ 2 = RAD ^ 2

If you plug various values of x into this equation, then you can calculate the corresponding values of y. Maybe start with X0=100, Y0=100, RAD=50 and x values that run from 50 to 150.

If you are familiar with sine and cosine, then a better solution for calculating the coordinates can be found using those; a web search will find descriptions of that approach.

[maja neskovic]

I have succed to make something doing what I needed. Thank you for your help.

This is the code:

 
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.geom.Arc2D;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import java.net.*;
import java.applet.Applet;
import java.awt.Font;
import java.awt.Event;

public class radnaverzija extends Applet implements Runnable {
    private static BasicStroke bs1 = new BasicStroke(3.0f);
    private Thread thread;
    private BufferedImage bimg;
    Font f = new Font("TimesRoman", Font.BOLD, 30);
    Font f1 = new Font("TimesRoman", Font.BOLD, 14);
    boolean frozen = false;

    CheckboxGroup p = new CheckboxGroup();
    Checkbox p1 = new Checkbox ("Ubrzajte zeca", p, false);
    Checkbox p2 = new Checkbox ("Usporite zeca", p, true);
    Choice span = new Choice();
    Button start;
    Button promena;
    Button ubrzajte;
    FlowLayout lm = new FlowLayout(FlowLayout.RIGHT);

    public void init() {
        setFont(f);
        setBackground(new Color(60,179,113 ));
        setFont(f1);


        arc1 = new Arc2D.Double(140, 140, 470, 330, 0, d, Arc2D.OPEN);
        URL slika;
        try {
            slika = new URL("http://www.wolflodge.org/prophecy/endofdays_2/White_Rabbit.gif");
            try {
                bmp = ImageIO.read(slika);
            } catch (IOException ex) {
                Logger.getLogger(forpetlja.class.getName()).log(Level.SEVERE, null, ex);
            }
        } catch (MalformedURLException ex) {
            Logger.getLogger(forpetlja.class.getName()).log(Level.SEVERE, null, ex);
        }

        x = 50;
        y = 50;
        w = 100;
        h = 100;
        d = 0;
        brojElemenata = 30;
        brzina=10;
        korak = 140/brojElemenata;
        kretanje=1;
        setLayout(lm);
Button start = new Button ("Start/Stop");
        add(start);
                        Button ubrzajte = new Button ("Ubrzajte zeca");
                add(ubrzajte);
                Button promena = new Button ("Promena terena");
        add(promena);
    }

    int x;
    int y;
    int w;
    int h;
    int d;
    int brojElemenata;
    int korak;
    int brzina;
    int kretanje;
    Arc2D arc1;
    BufferedImage bmp;
    File bmpFile;
    int counter;

 public boolean action (Event evt, Object arg)
  { if (evt.target instanceof Button) {
        String labl = (String) arg;
        if (labl.equals("Start/Stop"))
            if (frozen) {
          frozen = false;
          start();
          return false;
        } else {
          frozen = true;
          stop();
          return true;
            }
        else if (labl.equals("Promena terena"))
            setBackground(Color.GRAY);
        else if (labl.equals("Ubrzajte zeca"))
                    korak = 360/brojElemenata;


    }
    return true;
   }



  public void render(int w, int h, Graphics2D g2) {

        if(d>360 || d<0)
            {
               if(kretanje==1)
               kretanje=1;
              }
        if(kretanje==1)
        d+=korak;
        else
        d-=korak;
        arc1.setAngleExtent(-d);
        g2.draw(arc1);

        Point2D pt1 = arc1.getEndPoint();
        g2.setColor(new Color(105,105,105));
        if (g2.getBackground() == Color.GRAY  ) {
        g2.setColor(new Color(47,79,79));
        g2.drawArc(100, 100, 550, 450, 0, 360);
        g2.drawArc(150, 150, 450, 350, 0, 360);
        }
        if (g2.getBackground() == (new Color(60,179,113 ))  ) {
        g2.setColor(new Color(60,179,113 ));
        g2.drawArc(100, 100, 550, 450, 0, 360);
        g2.drawArc(150, 150, 450, 350, 0, 360);
        }
        g2.fillArc(100, 100, 550, 450, 0, 360);
        g2.setColor(new Color(60,179,113 ));
        g2.drawArc(100, 100, 550, 450, 0, 360);

        g2.drawArc(150, 150, 450, 350, 0, 360);
        g2.drawImage(bmp, new AffineTransform(1f,0f,0f,1f,pt1.getX()-(bmp.getHeight()/2),pt1.getY()-(bmp.getWidth()/2)), null);
        g2.setColor(Color.white);
        g2.setFont(f1);
        g2.drawString("Zec trči krug broj "+(d/360+1)+".", 70, 100);
    }

    public Graphics2D createGraphics2D(int w, int h) {
        Graphics2D g2 = null;
        if (bimg == null || bimg.getWidth() != w || bimg.getHeight() != h) {
            bimg = (BufferedImage) createImage(w, h);
        }
        g2 = bimg.createGraphics();
        g2.setStroke(bs1);
        g2.setBackground(getBackground());
        g2.clearRect(0, 0, w, h);
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);

        //g2.translate(50, 70);
        return g2;
    }

    public void update (Graphics g2) {
        paint(g2);
    }
    public void paint(Graphics g) {

	Dimension d = getSize();
        Graphics2D g2 = createGraphics2D(d.width, d.height);
        render(d.width, d.height, g2);
        g.drawImage(bimg, 0, 0, this);
        g2.dispose();

    }

    public void start() {
        thread = new Thread(this);
        thread.setPriority(Thread.MIN_PRIORITY);
        thread.start();
    }

    public synchronized void stop() {
        thread = null;
    }

    public void run() {
        Thread me = Thread.currentThread();
        while (thread == me) {
            repaint();
            try {
                thread.sleep(brzina);
            } catch (InterruptedException e) { break; }
        }
        thread = null;
    }
}


   

I have an assignment to make this applet connected with the database. I think to make connection with MySQL database. Can you explain me how to do it, please?