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.
Instances of ThreadLocalRandom are not cryptographically
secure. Consider instead using SecureRandom
in security-sensitive applications. Additionally,
default-constructed instances do not use a cryptographically random
seed unless the system property
java.util.secureRandomSeed is set to true.
| Modifier and Type | Method and Description |
|---|---|
static ThreadLocalRandom |
current()
Returns the current thread's
ThreadLocalRandom. |
DoubleStream |
doubles()
Returns an effectively unlimited stream of pseudorandom
double values, each between zero (inclusive) and one
(exclusive). |
DoubleStream |
doubles(double randomNumberOrigin,
double randomNumberBound)
Returns an effectively unlimited stream of pseudorandom
double values, each conforming to the given origin (inclusive) and bound
(exclusive). |
DoubleStream |
doubles(long streamSize)
Returns a stream producing the given
streamSize number of
pseudorandom double values, each between zero
(inclusive) and one (exclusive). |
DoubleStream |
doubles(long streamSize,
double randomNumberOrigin,
double randomNumberBound)
Returns a stream producing the given
streamSize number of
pseudorandom double values, each conforming to the given origin
(inclusive) and bound (exclusive). |
IntStream |
ints()
Returns an effectively unlimited stream of pseudorandom
int
values. |
IntStream |
ints(int randomNumberOrigin,
int randomNumberBound)
Returns an effectively unlimited stream of pseudorandom
int values, each conforming to the given origin (inclusive) and bound
(exclusive). |
IntStream |
ints(long streamSize)
Returns a stream producing the given
streamSize number of
pseudorandom int values. |
IntStream |
ints(long streamSize,
int randomNumberOrigin,
int randomNumberBound)
Returns a stream producing the given
streamSize number
of pseudorandom int values, each conforming to the given
origin (inclusive) and bound (exclusive). |
LongStream |
longs()
Returns an effectively unlimited stream of pseudorandom
long
values. |
LongStream |
longs(long streamSize)
Returns a stream producing the given
streamSize number of
pseudorandom long values. |
LongStream |
longs(long randomNumberOrigin,
long randomNumberBound)
Returns an effectively unlimited stream of pseudorandom
long values, each conforming to the given origin (inclusive) and bound
(exclusive). |
LongStream |
longs(long streamSize,
long randomNumberOrigin,
long randomNumberBound)
Returns a stream producing the given
streamSize number of
pseudorandom long, each conforming to the given origin
(inclusive) and bound (exclusive). |
protected int |
next(int bits)
Generates the next pseudorandom number.
|
boolean |
nextBoolean()
Returns a pseudorandom
boolean value. |
double |
nextDouble()
Returns a pseudorandom
double value between zero
(inclusive) and one (exclusive). |
double |
nextDouble(double bound)
Returns a pseudorandom
double value between 0.0
(inclusive) and the specified bound (exclusive). |
double |
nextDouble(double origin,
double bound)
Returns a pseudorandom
double value between the specified
origin (inclusive) and bound (exclusive). |
float |
nextFloat()
Returns a pseudorandom
float value between zero
(inclusive) and one (exclusive). |
double |
nextGaussian()
Returns the next pseudorandom, Gaussian ("normally") distributed
double value with mean 0.0 and standard
deviation 1.0 from this random number generator's sequence. |
int |
nextInt()
Returns a pseudorandom
int value. |
int |
nextInt(int bound)
Returns a pseudorandom
int value between zero (inclusive)
and the specified bound (exclusive). |
int |
nextInt(int origin,
int bound)
Returns a pseudorandom
int value between the specified
origin (inclusive) and the specified bound (exclusive). |
long |
nextLong()
Returns a pseudorandom
long value. |
long |
nextLong(long bound)
Returns a pseudorandom
long value between zero (inclusive)
and the specified bound (exclusive). |
long |
nextLong(long origin,
long bound)
Returns a pseudorandom
long value between the specified
origin (inclusive) and the specified bound (exclusive). |
void |
setSeed(long seed)
Throws
UnsupportedOperationException. |
public static ThreadLocalRandom current()
ThreadLocalRandom.ThreadLocalRandompublic void setSeed(long seed)
UnsupportedOperationException. Setting seeds in
this generator is not supported.setSeed in class Randomseed - the initial seedUnsupportedOperationException - alwaysprotected int next(int bits)
RandomThe 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 low-order
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 value.public int nextInt(int bound)
int value between zero (inclusive)
and the specified bound (exclusive).nextInt in class Randombound - the upper bound (exclusive). Must be positive.int value between zero
(inclusive) and the bound (exclusive)IllegalArgumentException - if bound is not positivepublic int nextInt(int origin,
int bound)
int value between the specified
origin (inclusive) and the specified bound (exclusive).origin - the least value returnedbound - the upper bound (exclusive)int value between the origin
(inclusive) and the bound (exclusive)IllegalArgumentException - if origin is greater than
or equal to boundpublic long nextLong()
long value.public long nextLong(long bound)
long value between zero (inclusive)
and the specified bound (exclusive).bound - the upper bound (exclusive). Must be positive.long value between zero
(inclusive) and the bound (exclusive)IllegalArgumentException - if bound is not positivepublic long nextLong(long origin,
long bound)
long value between the specified
origin (inclusive) and the specified bound (exclusive).origin - the least value returnedbound - the upper bound (exclusive)long value between the origin
(inclusive) and the bound (exclusive)IllegalArgumentException - if origin is greater than
or equal to boundpublic double nextDouble()
double value between zero
(inclusive) and one (exclusive).nextDouble in class Randomdouble value between zero
(inclusive) and one (exclusive)Math.random()public double nextDouble(double bound)
double value between 0.0
(inclusive) and the specified bound (exclusive).bound - the upper bound (exclusive). Must be positive.double value between zero
(inclusive) and the bound (exclusive)IllegalArgumentException - if bound is not positivepublic double nextDouble(double origin,
double bound)
double value between the specified
origin (inclusive) and bound (exclusive).origin - the least value returnedbound - the upper bound (exclusive)double value between the origin
(inclusive) and the bound (exclusive)IllegalArgumentException - if origin is greater than
or equal to boundpublic boolean nextBoolean()
boolean value.nextBoolean in class Randomboolean valuepublic float nextFloat()
float value between zero
(inclusive) and one (exclusive).public double nextGaussian()
Randomdouble value with mean 0.0 and standard
deviation 1.0 from this random number generator's sequence.
The general contract of nextGaussian is that one
double value, chosen from (approximately) the usual
normal distribution with mean 0.0 and standard deviation
1.0, is pseudorandomly generated and returned.
The method nextGaussian is implemented by class
Random as if by a threadsafe version of the following:
private double nextNextGaussian;
private boolean haveNextNextGaussian = false;
public double nextGaussian() {
if (haveNextNextGaussian) {
haveNextNextGaussian = false;
return nextNextGaussian;
} else {
double v1, v2, s;
do {
v1 = 2 * nextDouble() - 1; // between -1.0 and 1.0
v2 = 2 * nextDouble() - 1; // between -1.0 and 1.0
s = v1 * v1 + v2 * v2;
} while (s >= 1 || s == 0);
double multiplier = StrictMath.sqrt(-2 * StrictMath.log(s)/s);
nextNextGaussian = v2 * multiplier;
haveNextNextGaussian = true;
return v1 * multiplier;
}
}
This uses the polar method of G. E. P. Box, M. E. Muller, and
G. Marsaglia, as described by Donald E. Knuth in The Art of
Computer Programming, Volume 3: Seminumerical Algorithms,
section 3.4.1, subsection C, algorithm P. Note that it generates two
independent values at the cost of only one call to StrictMath.log
and one call to StrictMath.sqrt.nextGaussian in class Randomdouble value with mean 0.0 and
standard deviation 1.0 from this random number
generator's sequencepublic IntStream ints(long streamSize)
streamSize number of
pseudorandom int values.ints in class RandomstreamSize - the number of values to generateint valuesIllegalArgumentException - if streamSize is
less than zeropublic IntStream ints()
int
values.public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound)
streamSize number
of pseudorandom int values, each conforming to the given
origin (inclusive) and bound (exclusive).ints in class RandomstreamSize - the number of values to generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valueint values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if streamSize is
less than zero, or randomNumberOrigin
is greater than or equal to randomNumberBoundpublic IntStream ints(int randomNumberOrigin, int randomNumberBound)
int values, each conforming to the given origin (inclusive) and bound
(exclusive).ints in class Randomints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).randomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valueint values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if randomNumberOrigin
is greater than or equal to randomNumberBoundpublic LongStream longs(long streamSize)
streamSize number of
pseudorandom long values.longs in class RandomstreamSize - the number of values to generatelong valuesIllegalArgumentException - if streamSize is
less than zeropublic LongStream longs()
long
values.public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound)
streamSize number of
pseudorandom long, each conforming to the given origin
(inclusive) and bound (exclusive).longs in class RandomstreamSize - the number of values to generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuelong values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if streamSize is
less than zero, or randomNumberOrigin
is greater than or equal to randomNumberBoundpublic LongStream longs(long randomNumberOrigin, long randomNumberBound)
long values, each conforming to the given origin (inclusive) and bound
(exclusive).longs in class Randomlongs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).randomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuelong values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if randomNumberOrigin
is greater than or equal to randomNumberBoundpublic DoubleStream doubles(long streamSize)
streamSize number of
pseudorandom double values, each between zero
(inclusive) and one (exclusive).doubles in class RandomstreamSize - the number of values to generatedouble valuesIllegalArgumentException - if streamSize is
less than zeropublic DoubleStream doubles()
double values, each between zero (inclusive) and one
(exclusive).public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)
streamSize number of
pseudorandom double values, each conforming to the given origin
(inclusive) and bound (exclusive).doubles in class RandomstreamSize - the number of values to generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuedouble values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if streamSize is
less than zeroIllegalArgumentException - if randomNumberOrigin
is greater than or equal to randomNumberBoundpublic DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
double values, each conforming to the given origin (inclusive) and bound
(exclusive).doubles in class Randomdoubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).randomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuedouble values,
each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if randomNumberOrigin
is greater than or equal to randomNumberBound Submit a bug or feature
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