[prog] Seeking and appropriate Java component

[Riccarda Cassini]

Sue Stones wrote:
> Another problem with the program, is that all the particles drift to
> the north west.  I am using "Random" to produce the movements, but
> clearly "Random is biased.  Any one know the solution to this?  Here
> are the calls to Random.
> 
>   protected final Random rng = new Random();
> 
>   public synchronized void move() {
>     x += rng.nextInt(10) - 5;
>     y += rng.nextInt(20) - 10;
>   } // move


Hey, a question I can actually *answer*!  :-)

I think the bias is created by the way the method nextInt(n) is
defined:  it returns an int value between 0 (inclusive) and n
(*exclusive*).  Thus, for nextInt(10) you get values from 0..9. 
Or, after subtracting 5, you have -5..+4, which surely is biased.  
By using integers, you're essentially loosing 1 from the requested 
range n (on the upper bound).

Using "rng.nextInt(11) - 5" should solve the problem, as you'll then 
get values ranging from -5..+5.


Wiser heads than mine will have to comment on your other problem, though.

Ciao,

Riccarda



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