Solved

Help with java applet

Posted on 2001-07-04
12
166 Views
Last Modified: 2013-11-23
I have created a java applet and htm file called Checker4 which is a checker which consists of 4 fillRectangles. A top left, top right, bottom left and bottom right. The applet box is 200 width and 200 height. I also have a drawOval which is width 90 and height 90. The problem is that I need the drawOval to start at the top left box znd visit the top right, bottom right, bottom left and back to the top left rectanlge. I have managed to make the drawOval visit the topleft, top right and bottom right but cannot progress any further to the bottom left and back to the top left rectangle. My code is as follows:

/* an applet which draws a continous moving checker*/

import java.awt.*;

public class Checker4 extends TaskingApplet
{
Image offscreenImage;
Graphics offscreenGraphics;
int xpos;//y co-ordinate
int ypos;//x co-ordinate

  public void init()
   {
     offscreenImage = createImage(this.size().width,
     this.size().height);
     offscreenGraphics = offscreenImage.getGraphics();
   }

   public void run()
    {
      while (true)
       {
          for (xpos = 5; xpos <=105; xpos = xpos + 5)
           {
             repaint();
             try (Thread.sleep(50);}
             catch (InterrupterdException e) {}
           }
          for (ypos = 105; ypos >5; ypos = xpos -5)
           {
              repaint();
              try {Thread.sleep(50);}
              catch (InterruptedException e) {}
           }
          for ( xpos = 105; xpos >0; xpos = ypos -5)
           {
               repaint();
               try {Thread.sleep(50);}
               catch (InterruptedException e) {}
           }
          for { ypos = 5; ypos <=105; ypos = xpos-5)
           {
                repaint();
                try {Thread.sleep (50);}
                catch (InterruptedException e) {}
           }
     }
}

public void update (Graphics g)
 {
   paint (g);
 }
public void paint (Graphics g)
       {
         offscreenGraphics.setColor(Color.black};
         offscreenGraphics.fillRect(0,0,100,100);
         offscreenGraphics.setColor(Color.white);
         offscreenGraphics.fillRect(100,0,100,100);
         offscreenGraphics.fillRect(101,10,100,100);
         offscreenGraphics.setColor(Color.black);
         offscreenGraphics.fillRect(101,101,100,100);
         //draw Checker
         offscreenGraphics.setColor(Color.blue);
         offscreenGraphics.fillOval(xpos,ypos,90,90);
         //copy the image to the screen
         g.drawImage(offscreenImage,0,0,this);

        }
}
       
 
I would appreciate if someone would look at my code and let me know what I am doing wrong and how I should implement my program so the drawOval travels from the topleft box in a clockwise direction. Thank you for your time.

Veneta        
0
Comment
Question by:Veneta
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 6
  • 5
12 Comments
 
LVL 27

Accepted Solution

by:
rrz earned 50 total points
ID: 6254010
You should show us the TaskingApplet code.
0
 
LVL 92

Expert Comment

by:objects
ID: 6254191
> for (ypos = 105; ypos >5; ypos = xpos -5)

It should say ypos = ypos - 2 (not xpos - 5).
As xpos isn't changing this loop will never end.

Same problem with the other for loops, only the first one seems correct.
0
 

Author Comment

by:Veneta
ID: 6255414
Thanks rrz,

The code for TaskingApplet is as follows:


public class TaskingApplet extends java.applet.Applet
{                          implents Runnable
       Thread task;//declare a variable to hold new thread
       
        public void init()
        {
        //put initialisation code here
        }

        public void start()//creates a new thread
        {
              if (task == null);
               {
                  task = new Thread(this);//create new thread
                   task.start();//call the thread's           start//method - dont confuse with//the applet's start method
     
         }
}
public void stop()//stop thread here
  {
        if (task!= null)
         {
             task stop();call its stop metod
             task = null;//ready for garbage collector
         }
  }

public void run()
  {
  //put main code here
  }
}
0
Get 15 Days FREE Full-Featured Trial

Benefit from a mission critical IT monitoring with Monitis Premium or get it FREE for your entry level monitoring needs.
-Over 200,000 users
-More than 300,000 websites monitored
-Used in 197 countries
-Recommended by 98% of users

 
LVL 27

Expert Comment

by:rrz
ID: 6256156
You had a lot of mistakes in your code. I made the necessary changes.
public class TaskingApplet extends java.applet.Applet implements Runnable
{                                                    
      Thread task;
       public void start()
       {
             if (task == null);
              {
                 task = new Thread(this);
                  task.start();
              }
       }
public void stop(){task = null;}
public void run(){}
}

import java.awt.*;
public class Checker4 extends TaskingApplet
{
Image offscreenImage;
Graphics offscreenGraphics;
int xpos=5;//y co-ordinate
int ypos=5;//x co-ordinate

 public void init()
  {
    offscreenImage = createImage(getSize().width,getSize().height);
    offscreenGraphics = offscreenImage.getGraphics();
  }

  public void run()
   {
     Thread thisthread = Thread.currentThread();
     while (task==thisthread)
      {
         for (xpos = 5; xpos <=105; xpos = xpos + 5)
          {
            repaint();
            try {Thread.sleep(50);}          
            catch (InterruptedException e) {}        
          }
         for ( ypos = 5; ypos <=105; ypos = ypos+5)
          {
             repaint();
             try {Thread.sleep(50);}
             catch (InterruptedException e) {}
          }
         for ( xpos = 105; xpos >0; xpos = xpos -5)
          {
              repaint();
              try {Thread.sleep(50);}
              catch (InterruptedException e) {}
          }
         for (ypos = 105; ypos >5; ypos = ypos -5)
          {
               repaint();
               try {Thread.sleep (50);}
               catch (InterruptedException e) {}
          }
      }
   }

public void update (Graphics g)
{
  paint (g);
}
public void paint (Graphics g)
      {
        offscreenGraphics.setColor(Color.black);
        offscreenGraphics.fillRect(0,0,100,100);
        offscreenGraphics.setColor(Color.white);
        offscreenGraphics.fillRect(100,0,100,100);
        offscreenGraphics.fillRect(0,100,100,100);
        offscreenGraphics.setColor(Color.black);
        offscreenGraphics.fillRect(101,101,100,100);
        //draw Checker
        offscreenGraphics.setColor(Color.blue);
        offscreenGraphics.fillOval(xpos,ypos,90,90);
        //copy the image to the screen
        g.drawImage(offscreenImage,0,0,this);

       }  
}
I would appreciate some points.
 rrz
0
 
LVL 92

Expert Comment

by:objects
ID: 6257633
rrz,
But basically your providing the same answer I did :)
0
 
LVL 27

Expert Comment

by:rrz
ID: 6257820
Yes,objects your comments were correct. But Veneta had a lot more mistakes than the ones you pointed out. I think he(or she) took the program from the book: Sam's "Teach Yourself Java in 21 days" and attempted to dress it up some. I guess it is a good way to learn. My suggestion to Veneta is to take smaller gulps next time. Just try to learn one thing at a time. rrz
0
 
LVL 92

Expert Comment

by:objects
ID: 6257846
And there are others that you also missed.
I was just focussing on the question at hand, ie. one step at a time :)
0
 
LVL 27

Expert Comment

by:rrz
ID: 6258146
What did I miss? I realize that you have much more experience than I do. I am willing to give points to learn something.  rrz
0
 
LVL 27

Expert Comment

by:rrz
ID: 6258168
What did I miss? I realize that you have much more experience than I do. I am willing to give points to learn something.  rrz
0
 
LVL 92

Expert Comment

by:objects
ID: 6258169
Main change I'd make would be to move the painting of the offscreen image out of paint.
And probably factoring out, some of the 'static' painting from the 'dynamic' painting.
The thread exit code could also be improved to stop immediatly instead of once the animation loop is complete.
0
 
LVL 27

Expert Comment

by:rrz
ID: 6258429
Why would we want "to move the painting of the offscreen image out of paint"?  What 'static' painting are you referring to? Are you referring to fact the checker is at most in front 2 squares at any point in time? The thread(in my code) stops when the applet stops. The animation is never complete. The checker keeps repeating its path.
rrz
0
 
LVL 92

Expert Comment

by:objects
ID: 6258440
The offscreen image gets (unnecessarily) repainted every time repaint is called, it only need to be repainted when the oval movesThe thread (in your code) won't stop until the oval has finished moving around the board.

Most of these are trivial changes and will have no real impact on this simple case but
0

Featured Post

Creating Instructional Tutorials  

For Any Use & On Any Platform

Contextual Guidance at the moment of need helps your employees/users adopt software o& achieve even the most complex tasks instantly. Boost knowledge retention, software adoption & employee engagement with easy solution.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction Java can be integrated with native programs using an interface called JNI(Java Native Interface). Native programs are programs which can directly run on the processor. JNI is simply a naming and calling convention so that the JVM (Java…
In this post we will learn different types of Android Layout and some basics of an Android App.
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…
This tutorial will introduce the viewer to VisualVM for the Java platform application. This video explains an example program and covers the Overview, Monitor, and Heap Dump tabs.

688 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question