Returns a
double value with a positive sign, greater
than or equal to
0.0 and less than
1.0.
Returned values are chosen pseudorandomly with (approximately)
uniform distribution from that range.
When this method is first called, it creates a single new
pseudorandom-number generator, exactly as if by the expression
new java.util.Random
This new pseudorandom-number generator is used thereafter for all
calls to this method and is used nowhere else.
This method is properly synchronized to allow correct use by more
than one thread. However, if many threads need to generate
pseudorandom numbers at a great rate, it may reduce contention for
each thread to have its own pseudorandom-number generator.