public class ThreadLocalRandom extends Random
Random
generator used by the Math
class, a ThreadLocalRandom
is initialized
with an internally generated seed that may not otherwise be
modified. When applicable, use of ThreadLocalRandom
rather
than shared Random
objects in concurrent programs will
typically encounter much less overhead and contention. Use of
ThreadLocalRandom
is particularly appropriate when multiple
tasks (for example, each a ForkJoinTask
) use random numbers
in parallel in thread pools.
Usages of this class should typically be of the form:
ThreadLocalRandom.current().nextX(...)
(where
X
is Int
, Long
, etc).
When all usages are of this form, it is never possible to
accidently share a ThreadLocalRandom
across multiple threads.
This class also provides additional commonly used bounded random generation methods.
Modifier and Type  Method and Description 

static ThreadLocalRandom 
current()
Returns the current thread's
ThreadLocalRandom . 
protected int 
next(int bits)
Generates the next pseudorandom number.

double 
nextDouble(double n)
Returns a pseudorandom, uniformly distributed
double value
between 0 (inclusive) and the specified value (exclusive). 
double 
nextDouble(double least,
double bound)
Returns a pseudorandom, uniformly distributed value between the
given least value (inclusive) and bound (exclusive).

int 
nextInt(int least,
int bound)
Returns a pseudorandom, uniformly distributed value between the
given least value (inclusive) and bound (exclusive).

long 
nextLong(long n)
Returns a pseudorandom, uniformly distributed value
between 0 (inclusive) and the specified value (exclusive).

long 
nextLong(long least,
long bound)
Returns a pseudorandom, uniformly distributed value between the
given least value (inclusive) and bound (exclusive).

void 
setSeed(long seed)
Throws
UnsupportedOperationException . 
nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong
public static ThreadLocalRandom current()
ThreadLocalRandom
.ThreadLocalRandom
public void setSeed(long seed)
UnsupportedOperationException
. Setting seeds in
this generator is not supported.setSeed
in class Random
seed
 the initial seedUnsupportedOperationException
 alwaysprotected int next(int bits)
Random
The general contract of next
is that it returns an
int
value and if the argument bits
is between
1
and 32
(inclusive), then that many loworder
bits of the returned value will be (approximately) independently
chosen bit values, each of which is (approximately) equally
likely to be 0
or 1
. The method next
is
implemented by class Random
by atomically updating the seed to
(seed * 0x5DEECE66DL + 0xBL) & ((1L << 48)  1)
and returning
(int)(seed >>> (48  bits))
.
This is a linear congruential pseudorandom number generator, as
defined by D. H. Lehmer and described by Donald E. Knuth in
The Art of Computer Programming, Volume 3:
Seminumerical Algorithms, section 3.2.1.public int nextInt(int least, int bound)
least
 the least value returnedbound
 the upper bound (exclusive)IllegalArgumentException
 if least greater than or equal
to boundpublic long nextLong(long n)
n
 the bound on the random number to be returned. Must be
positive.IllegalArgumentException
 if n is not positivepublic long nextLong(long least, long bound)
least
 the least value returnedbound
 the upper bound (exclusive)IllegalArgumentException
 if least greater than or equal
to boundpublic double nextDouble(double n)
double
value
between 0 (inclusive) and the specified value (exclusive).n
 the bound on the random number to be returned. Must be
positive.IllegalArgumentException
 if n is not positivepublic double nextDouble(double least, double bound)
least
 the least value returnedbound
 the upper bound (exclusive)IllegalArgumentException
 if least greater than or equal
to bound Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developertargeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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