Re: random real number between 0 (inclusive) and 1 (inclusive)

From:
Eric Sosman <Eric.Sosman@sun.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 07 Nov 2007 10:49:58 -0500
Message-ID:
<1194450602.57898@news1nwk>
Patricia Shanahan wrote On 11/06/07 20:38,:

Dr J R Stockton wrote:
[...]

Is nextDouble based on *A* specific PRNG, or is it based on whichever
PRNG the system author happened to like? In the latter case, your
question may have multiple answers.


Random's nextDouble is specified to be based on this method:

synchronized protected int next(int bits) {
        seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);
        return (int)(seed >>> (48 - bits));
  }

seed is a long.

Each call to nextDouble uses a next(26) and a next(27).

You can see a lot of this information in the Random API documentation at
http://java.sun.com/j2se/1.5.0/docs/api/java/util/Random.html


    Note that java.util.Random is not final, and neither
is its next() method. This is (presumably) deliberate:
by extending Random and reimplementing next(), one can
get Random's nextDouble() et al. to use a different PRNG.
(java.util.SecureRandom does exactly this, although it
also overrides and/or adds some other methods, too.)

--
Eric.Sosman@sun.com

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