Don't read the file in draw() 60 times per second, do it once in setup().

See the loadStrings method. Then you can use a for loop to fill the array.

Well, the code above is OK... if you want to show a progressive result. The file isn't read wholly on each frame, but only one line is read on each frame.
The problem is that draw() continue to be called after the end of the file...

Some other issues:
- You define the size of the array at 313, but apparently you need only 313 / 3 entries.
- If the data really looks like that, you can just generate it. But perhaps you didn't show the real values.
- The while at line 18 isn't useful, a simple if would have done the job...
- And, well, indeed, loadStrings() is here to ease your life... It would avoid the AIOOB exception, since you cannot read past the end of the file.

thanks guys..you are my teachers..
I post the new code here..Hope it could help other people with the same problem as me..If the code could be improven, please do tell..

1. String rows[] = loadStrings("Head.txt");
   
2. String[] columns;
   
3. columns = splitTokens(rows[1]);
   
4. double[][] matrixA = new double[rows.length][columns.length];
   
5. 
   
6. println("there are " + rows.length + " rows");
   
7. println("there are " + columns.length + " columns");
   
8. 
   
9. //insert the numbers from txt file into matrixA
   
10. for (int i =0 ; i<rows.length; i++){
    
11.   columns = splitTokens(rows[i]);
    
12.   for(int j=0; j<columns.length; j++){
    
13.     matrixA[i][j] = Double.parseDouble(columns[j]);
    
14.   }
    
15. }
    
16.  
    
17. //check what's inside matrixA
    
18. for(int i=0; i<rows.length; i++){
    
19.   for(int j=0; j<columns.length; j++){
    
20.     print(matrixA[i][j] + "\t");
    
21.   }
    
22.   print("\n");
    
23. }
    
24. 
    

I got other questions here..There are libraries(JAVA's) for matrices operation such as EJML, JAMA etc..
I would like to use those so its easier to calculate matrices..but the problem is I dont know how to use it
for eg..
read the txt file and directly insert the numbers to the matrix that is created by the classess in the library..
Could someone whose experienced or know about this help??any ideas are appreciated..