Random Lines

[Urgle]

Im trying to make an applet that draws 100 random lines, one at a time.
I new to applets and I have a feeling im not doing this right? Heres what I have:

package saver1;

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

public class saver1 extends Applet {
int width;
int height ;
private int randomX1()
{ 
   return ( int ) ( Math.random() * width ); 
}

private int randomY1()
{ 
   return ( int ) ( Math.random() * height ); 
}
private int randomX2()
{ 
   return ( int ) ( Math.random() * width ); 
}

private int randomY2()
{ 
   return ( int ) ( Math.random() * height ); 
}

	

	public static void main(String[] args) {}
		public void paint(Graphics g)
		  {
		    
		    
		for ( int x = 0; x<100; x++ ){
			g.drawLine(randomX1(), randomY1(), randomX2(), randomY2()); 
		}

	}

}

[Eranga]

First of write a simple application/applet to draw a single line. The way you have work out is completely wrong. Here is a simple example. See how I workout there.

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

public class DrawingLines extends Applet {

   int width, height;

   public void init() {
      width = getSize().width;
      height = getSize().height;
      setBackground( Color.black );
   }

   public void paint( Graphics g ) {
      g.setColor( Color.green );
      for ( int i = 0; i < 10; ++i ) {
         g.drawLine( width, height, i * width / 10, 0 );
      }
   }
}

[emceenugget]

What happens when you run it?

[Urgle]

how would I incorperate randoms into the g.drawline?

[Urgle]

ok, I figured out how to draw 100 random lines but how do I change it to draw them one at a time instead of all at the same time?

package saver1;

import java.applet.*;
import java.awt.*;
import java.util.Random;

public class saver1 extends Applet {

   int width, height;
Random rnd = new Random();
   public void init() {
      width = getSize().width;
      height = getSize().height;
      setBackground( Color.black );
   }

   public void paint( Graphics g ) {
      g.setColor( Color.green );
      for ( int i = 0; i < 100; ++i ) {
    	  int x1 = rnd.nextInt( getSize().width );
          int y1 = rnd.nextInt( getSize().height );
          int x2 = rnd.nextInt( getSize().width );
          int y2 = rnd.nextInt( getSize().height );
         
    	  g.drawLine( x1, y1, x2, y2 );
      }
   }
}

[Eranga]

Do you know about Threads in Java?

[Urgle]

no, but i know that they have something to do with the path of execution

[Eranga]

no, but i know that they have something to do with the path of execution

With what? Threads?

[Urgle]

yea with threads

[Eranga]

Ok, basically thread are unit of a program execution. You can have multiple such units. In case of you application we can think about that in this way.

One unit for the drawing lines, and one unit for the display one by one.

Do you know more about thread? There are two ways to do that. Using Thread class or Runnable interface. If you can do a simple example on Threads first of all, it's much better.

[Urgle]

since I know almost nothing about threads Im not sure how to make my program use them

[Eranga]

To do such things we have only two choices. Swing timer and Threads. Nothing to do with Swing timer here in your application. Only option is Threads. That's the easiest way.

[Urgle]

I understand I need to use threads but how?

[Eranga]

I understand I need to use threads but how?

That what you should lean. About threads.

[Eranga]

I've change that my previous code according to your requirement. Try to identify what's going on there.

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

public class DrawingLines extends Applet implements Runnable {

    int width, height;
    int i = 0;
    Thread t = null;
    boolean threadSuspended;

    public void init() {
        width = getSize().width;
        height = getSize().height;
        setBackground( Color.black );
    }

    public void paint( Graphics g ) {
      g.setColor( Color.green );
      g.drawLine( width, height, i * width / 10, 0 );
    }

    public void start() {
        if ( t == null ) {
            t = new Thread( this );
            threadSuspended = false;
            t.start();
        }
        else {
            if ( threadSuspended ) {
                threadSuspended = false;
                synchronized( this ) {
                    notify();
                }
            }
        }
    }
   
    public void run() {
        try {
            while(true) {
                ++i;
                if(i ==10) {
                    i = 0;
                }
                
                if(threadSuspended) {
                    synchronized(this) {
                        while(threadSuspended) {
                            wait();
                        }
                    }
                }
                repaint();
                t.sleep(1000);
            }
        }
        catch(InterruptedException ex) {
            
        }
    }
}

[Urgle]

so basicly what youve done is made it pause after each line and then call repaint to paint the next line?

[Urgle]

ive modified my code to this but im getting some syntax errors that i dont know how to fix.

package saver1;

import java.applet.*;
import java.awt.*;
import java.util.Random;

public class saver1 extends Applet {

    int width, height;
    int i = 0;
    Thread t = null;
    boolean threadSuspended;
    Random rnd = new Random();

    public void init() {
        width = getSize().width;
        height = getSize().height;
        setBackground( Color.black );
    }
public void paint( Graphics g ) {
      g.setColor( Color.green );
      for ( int i = 0; i < 100; ++i ) {
    	  int x1 = rnd.nextInt( getSize().width );
          int y1 = rnd.nextInt( getSize().height );
          int x2 = rnd.nextInt( getSize().width );
          int y2 = rnd.nextInt( getSize().height );
         
    	  [U]g.drawLine( x1, y1, x2, y2 ); // <- SYNTAX ERROR[/U]
      }
    

    public void start() {
        if ( t == null ) {
            [U]t = new Thread( this ); // <- SYNTAX ERROR[/U]
            threadSuspended = false;
            t.start();
        }
        else {
            if ( threadSuspended ) {
                threadSuspended = false;
                synchronized( this ) {
                    notify();
                }
            }
        }
    }
   
    public void run() {
        try {
            while(true) {
                ++i;
                if(i ==10) {
                    i = 0;
                }
                
                if(threadSuspended) {
                    synchronized(this) {
                        while(threadSuspended) {
                            wait();
                        }
                    }
                }
                repaint();
                t.sleep(1000);
            }
        }
        catch(InterruptedException ex) {
            
        }
    }
}

[Eranga]

so basicly what youve done is made it pause after each line and then call repaint to paint the next line?

Yes, you got the point. That's the final thing we have do is.

[Urgle]

hmm i think i fixed the syntax but now it just updates once a second, still doesnt draw one at a time

[Eranga]

still stumped on the syntax errors above

Yes you have done couple of mistakes in your code.

1. You didn't implement the Runnable interface.

public class saver1 extends Applet implements Runnable {

2. Misses the ending } in paint(Graphics g) method.

Correct them and see what happen.