A random number generator isolated to the current thread. Like the
global 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 {@linkplain System#getProperty system property}
java.util.secureRandomSeed
is set to true
.
Public Method Summary
static ThreadLocalRandom |
current()
Returns the current thread's
ThreadLocalRandom . |
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). |
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()
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). |
IntStream |
ints(long streamSize)
Returns a stream producing the given
streamSize number 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()
Returns an effectively unlimited stream 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(long streamSize)
Returns a stream producing the given
streamSize number of
pseudorandom long values. |
LongStream |
longs()
Returns an effectively unlimited stream 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). |
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(int origin, int bound)
Returns a pseudorandom
int value between the specified
origin (inclusive) and the specified bound (exclusive). |
int |
nextInt()
Returns a pseudorandom
int value. |
int |
nextInt(int bound)
Returns a pseudorandom
int 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). |
long |
nextLong(long bound)
Returns a pseudorandom
long value between zero (inclusive)
and the specified bound (exclusive). |
long |
nextLong()
Returns a pseudorandom
long value. |
void |
setSeed(long seed)
Throws
UnsupportedOperationException . |
Protected Method Summary
int |
next(int bits)
Generates the next pseudorandom number.
|
Inherited Method Summary
Public Methods
public static ThreadLocalRandom current ()
Returns the current thread's ThreadLocalRandom
.
Returns
- the current thread's
ThreadLocalRandom
public 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).
Parameters
streamSize | the number of values to generate |
---|---|
randomNumberOrigin | the origin (inclusive) of each random value |
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
double
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if streamSize is
less than zero |
---|---|
IllegalArgumentException | if randomNumberOrigin
is greater than or equal to randomNumberBound |
public DoubleStream doubles (long streamSize)
Returns a stream producing the given streamSize
number of
pseudorandom double
values, each between zero
(inclusive) and one (exclusive).
Parameters
streamSize | the number of values to generate |
---|
Returns
- a stream of
double
values
Throws
IllegalArgumentException | if streamSize is
less than zero |
---|
public DoubleStream doubles ()
Returns an effectively unlimited stream of pseudorandom double
values, each between zero (inclusive) and one
(exclusive).
Returns
- a stream of pseudorandom
double
values
public 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).
Parameters
randomNumberOrigin | the origin (inclusive) of each random value |
---|---|
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
double
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if randomNumberOrigin
is greater than or equal to randomNumberBound |
---|
public IntStream ints (long streamSize)
Returns a stream producing the given streamSize
number of
pseudorandom int
values.
Parameters
streamSize | the number of values to generate |
---|
Returns
- a stream of pseudorandom
int
values
Throws
IllegalArgumentException | if streamSize is
less than zero |
---|
public 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).
Parameters
randomNumberOrigin | the origin (inclusive) of each random value |
---|---|
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
int
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if randomNumberOrigin
is greater than or equal to randomNumberBound |
---|
public IntStream ints ()
Returns an effectively unlimited stream of pseudorandom int
values.
Returns
- a stream of pseudorandom
int
values
public 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).
Parameters
streamSize | the number of values to generate |
---|---|
randomNumberOrigin | the origin (inclusive) of each random value |
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
int
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if streamSize is
less than zero, or randomNumberOrigin
is greater than or equal to randomNumberBound |
---|
public LongStream longs (long streamSize)
Returns a stream producing the given streamSize
number of
pseudorandom long
values.
Parameters
streamSize | the number of values to generate |
---|
Returns
- a stream of pseudorandom
long
values
Throws
IllegalArgumentException | if streamSize is
less than zero |
---|
public LongStream longs ()
Returns an effectively unlimited stream of pseudorandom long
values.
Returns
- a stream of pseudorandom
long
values
public 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).
Parameters
randomNumberOrigin | the origin (inclusive) of each random value |
---|---|
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
long
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if randomNumberOrigin
is greater than or equal to randomNumberBound |
---|
public 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).
Parameters
streamSize | the number of values to generate |
---|---|
randomNumberOrigin | the origin (inclusive) of each random value |
randomNumberBound | the bound (exclusive) of each random value |
Returns
- a stream of pseudorandom
long
values, each with the given origin (inclusive) and bound (exclusive)
Throws
IllegalArgumentException | if streamSize is
less than zero, or randomNumberOrigin
is greater than or equal to randomNumberBound |
---|
public boolean nextBoolean ()
Returns a pseudorandom boolean
value.
Returns
- a pseudorandom
boolean
value
public double nextDouble ()
Returns a pseudorandom double
value between zero
(inclusive) and one (exclusive).
Returns
- a pseudorandom
double
value between zero (inclusive) and one (exclusive)
public double nextDouble (double bound)
Returns a pseudorandom double
value between 0.0
(inclusive) and the specified bound (exclusive).
Parameters
bound | the upper bound (exclusive). Must be positive. |
---|
Returns
- a pseudorandom
double
value between zero (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if bound is not positive
|
---|
public double nextDouble (double origin, double bound)
Returns a pseudorandom double
value between the specified
origin (inclusive) and bound (exclusive).
Parameters
origin | the least value returned |
---|---|
bound | the upper bound (exclusive) |
Returns
- a pseudorandom
double
value between the origin (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if origin is greater than
or equal to bound
|
---|
public float nextFloat ()
Returns a pseudorandom float
value between zero
(inclusive) and one (exclusive).
Returns
- a pseudorandom
float
value between zero (inclusive) and one (exclusive)
public 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.
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
.Returns
- the next pseudorandom, Gaussian ("normally") distributed
double
value with mean0.0
and standard deviation1.0
from this random number generator's sequence
public int nextInt (int origin, int bound)
Returns a pseudorandom int
value between the specified
origin (inclusive) and the specified bound (exclusive).
Parameters
origin | the least value returned |
---|---|
bound | the upper bound (exclusive) |
Returns
- a pseudorandom
int
value between the origin (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if origin is greater than
or equal to bound
|
---|
public int nextInt ()
Returns a pseudorandom int
value.
Returns
- a pseudorandom
int
value
public int nextInt (int bound)
Returns a pseudorandom int
value between zero (inclusive)
and the specified bound (exclusive).
Parameters
bound | the upper bound (exclusive). Must be positive. |
---|
Returns
- a pseudorandom
int
value between zero (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if bound is not positive
|
---|
public long nextLong (long origin, long bound)
Returns a pseudorandom long
value between the specified
origin (inclusive) and the specified bound (exclusive).
Parameters
origin | the least value returned |
---|---|
bound | the upper bound (exclusive) |
Returns
- a pseudorandom
long
value between the origin (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if origin is greater than
or equal to bound
|
---|
public long nextLong (long bound)
Returns a pseudorandom long
value between zero (inclusive)
and the specified bound (exclusive).
Parameters
bound | the upper bound (exclusive). Must be positive. |
---|
Returns
- a pseudorandom
long
value between zero (inclusive) and the bound (exclusive)
Throws
IllegalArgumentException | if bound is not positive
|
---|
public long nextLong ()
Returns a pseudorandom long
value.
Returns
- a pseudorandom
long
value
public void setSeed (long seed)
Throws UnsupportedOperationException
. Setting seeds in
this generator is not supported.
Parameters
seed | the initial seed |
---|
Throws
UnsupportedOperationException | always |
---|
Protected Methods
protected int next (int bits)
Generates the next pseudorandom number. Subclasses should override this, as this is used by all other methods.
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 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.Parameters
bits | random bits |
---|
Returns
- the next pseudorandom value from this random number generator's sequence