Re: random real number between 0 (inclusive) and 1 (inclusive)
Eric Sosman wrote:
Piotr Kobzda wrote:
[...]
But the problem here is, that the general purpose implementation must
extend the concrete Random implementation (which can not be anonymous
class). The best approach I can think of to achieve that might look
as follows: [...]
Encapsulation might be a better choice than extension,
and would certainly be less troublesome to code.
Yup, that's often a better choice.
public class FunnyRandom {
private final Random rand = new Random();
public double nextInclusiveDouble() {
// flawed implementation:
double r = rand.nextDouble();
return rand.nextBoolean() ? r : 1.0 - r;
}
}
If you wanted, you could add a constructor that supplies
a pre-existing Random instead of generating a new one, and/or
an access method to return a reference to the internal Random,
and assorted other decorations. But it doesn't seem to me
that there's any compelling reason that a generator of a
special distribution should also "be a" Random.
There is no real need to do so. The reason for me was to combine
default implementation of Random with encapsulated "accessor"
(BitsProvider) of the protected next() of Random. BTW, maybe better
would be calling it RandomDelegate instead of RandomExtend...
When we don't want delegation model (a bit tricky BTW, there are only
two methods delegated), we just don't need setSeed() in proposed
BitsProvider interface. However, "something" should still extend
concrete Random implementation in order to access its next(), otherwise
it must be simulated, e.g. using nextInt(), as proposed earlier by Patricia.
So, as long as an implementation does not needs the next() access (as in
your example) there is no need for Random extension.
(As discussed elsethread, the value of implementing this
particular special distribution is questionable. Also, even
though I proposed the algorithm shown here, I have since
realized that it is incorrect. As I wrote when I suggested it,
"trust, but verify.")
Well, there is no need for that in the _final_ problem of the OP, no
question on that. Proposed here is the solution of the _original_
problem, i.e. with no mention of taking just "two billion" distribution
(that's the goal added later by the OP). The proposed solution is just
to generate random sequence of doubles containing 1 with the same
(approximately) probability as for the other doubles. Do you think it's
incorrect for that?
piotr