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Thread: g.drawLine doesn't draw line in for loop

  1. #1
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    Default g.drawLine doesn't draw line in for loop

    I am really new to Java. As an exercise I'm trying to make an applet that draws "Cantor Dust" (L-system - Wikipedia, the free encyclopedia - third example. I filled an array with integers named A and B
    and used g.drawLine to try to draw a line at a spot proportional to the position in the array for every element that was "A".

    It compiles, but in Firefox I just get a blank screen

    Any help or pointers greatly appreciated!

    import java.awt.*;
    import java.lang.*;
    import java.util.*;
    public class CantorDust extends java.applet.Applet {
       static int A; //A and B are what the arrays are filled with. A = draw forward. B= move forward
       static int B;
       static int i; //i,j,k,l are "counters" in the for-loops.
       static int j;
       static int k;
       static int l;
       static int m; //m is just l+1. 
        static double iterations = 5.0;                           //#iterations
        static double sizeArray = Math.pow(3.0, iterations);      //Size of array is 3^#iter.      
        static int NsizeArray = (int)sizeArray;                   //convert double to int
        static int[] VDust = new int[NsizeArray];                 
        static int[] NDust = new int[NsizeArray];                //Declare two identical arrays
        static double lineSize;                                  //Size of line to draw
        static int NlineSize;                                    //same for int
        public void paint(Graphics g) {
            double lineSize = 600/NsizeArray;              //Line size - (for 5 iter should be 2.4)
    	int NlineSize = (int)lineSize;                       //convert to int.
    	for(i=0; i<iterations; i++)
    		for (j=1; j<NsizeArray;j++)      
    	     if (VDust[j]==A)
    		NDust[1+3*(j-1)]=A;                        //Fill NDust from VDust               
            	NDust[2+3*(j-1)]=B;                      //according to the rule A -> ABA
    	    if (VDust[j]==B)
    	        NDust[2+3*(j-1)]=B;                      //Fill NDust from VDust according
    	        NDust[3+3*(j-1)]=B;                   //to the rule B -> BBB
    	for (k=0;k<sizeArray;k++)                     //Form a new NDust by copying VDust
    	    VDust[k] = NDust[k];
    	for(l=0; l<sizeArray; l++)
    	  m = l++;
    	      g.drawLine(l*NlineSize,20,(m)*NlineSize,20);   //For every A element in NDust 
    	  // if(NDust[l]==B) do nothing.("move forward")     //draw a line of length Nlinesize    
    Last edited by copeg; October 12th, 2010 at 06:09 PM. Reason: Please use the code tags

  2. #2
    Administrator copeg's Avatar
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    Default Re: g.drawLine doesn't draw line in for loop

    Did you test this outside of a browser, say in AppletViewer? This will tell you if your code has any exceptions, which there are:
    Exception in thread "AWT-EventQueue-1" java.lang.ArrayIndexOutOfBoundsException: 244
    	at CantorDust.paint(CantorDust.java:29)

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