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public
class
ThreadLocalRandom
extends Random
java.lang.Object | ||
↳ | java.util.Random | |
↳ | java.util.concurrent.ThreadLocalRandom |
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 System#getProperty
java.util.secureRandomSeed
is set to true
.
Public methods | |
---|---|
static
ThreadLocalRandom
|
current()
Returns the current thread's |
DoubleStream
|
doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)
Returns a stream producing the given |
DoubleStream
|
doubles(long streamSize)
Returns a stream producing the given |
DoubleStream
|
doubles()
Returns an effectively unlimited stream of pseudorandom |
DoubleStream
|
doubles(double randomNumberOrigin, double randomNumberBound)
Returns an effectively unlimited stream of pseudorandom |
IntStream
|
ints(long streamSize)
Returns a stream producing the given |
IntStream
|
ints(int randomNumberOrigin, int randomNumberBound)
Returns an effectively unlimited stream of pseudorandom |
IntStream
|
ints()
Returns an effectively unlimited stream of pseudorandom |
IntStream
|
ints(long streamSize, int randomNumberOrigin, int randomNumberBound)
Returns a stream producing the given |
LongStream
|
longs(long streamSize)
Returns a stream producing the given |
LongStream
|
longs()
Returns an effectively unlimited stream of pseudorandom |
LongStream
|
longs(long randomNumberOrigin, long randomNumberBound)
Returns an effectively unlimited stream of pseudorandom |
LongStream
|
longs(long streamSize, long randomNumberOrigin, long randomNumberBound)
Returns a stream producing the given |
boolean
|
nextBoolean()
Returns a pseudorandom |
double
|
nextDouble()
Returns a pseudorandom |
double
|
nextDouble(double bound)
Returns a pseudorandom |
double
|
nextDouble(double origin, double bound)
Returns a pseudorandom |
float
|
nextFloat()
Returns a pseudorandom |
double
|
nextGaussian()
Returns the next pseudorandom, Gaussian ("normally") distributed
|
int
|
nextInt(int origin, int bound)
Returns a pseudorandom |
int
|
nextInt()
Returns a pseudorandom |
int
|
nextInt(int bound)
Returns a pseudorandom |
long
|
nextLong(long origin, long bound)
Returns a pseudorandom |
long
|
nextLong(long bound)
Returns a pseudorandom |
long
|
nextLong()
Returns a pseudorandom |
void
|
setSeed(long seed)
Throws |
Protected methods | |
---|---|
int
|
next(int bits)
Generates the next pseudorandom number. |
Inherited methods | |
---|---|
public static ThreadLocalRandom current ()
Returns the current thread's ThreadLocalRandom
.
Returns | |
---|---|
ThreadLocalRandom |
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 |
long : the number of values to generate |
randomNumberOrigin |
double : the origin (inclusive) of each random value |
randomNumberBound |
double : the bound (exclusive) of each random value |
Returns | |
---|---|
DoubleStream |
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 |
long : the number of values to generate |
Returns | |
---|---|
DoubleStream |
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).
doubles(Long.MAX_VALUE)
.Returns | |
---|---|
DoubleStream |
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).
doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.Parameters | |
---|---|
randomNumberOrigin |
double : the origin (inclusive) of each random value |
randomNumberBound |
double : the bound (exclusive) of each random value |
Returns | |
---|---|
DoubleStream |
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 |
long : the number of values to generate |
Returns | |
---|---|
IntStream |
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).
ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.Parameters | |
---|---|
randomNumberOrigin |
int : the origin (inclusive) of each random value |
randomNumberBound |
int : the bound (exclusive) of each random value |
Returns | |
---|---|
IntStream |
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.
ints(Long.MAX_VALUE)
.Returns | |
---|---|
IntStream |
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 |
long : the number of values to generate |
randomNumberOrigin |
int : the origin (inclusive) of each random value |
randomNumberBound |
int : the bound (exclusive) of each random value |
Returns | |
---|---|
IntStream |
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 |
long : the number of values to generate |
Returns | |
---|---|
LongStream |
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.
longs(Long.MAX_VALUE)
.Returns | |
---|---|
LongStream |
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).
longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.Parameters | |
---|---|
randomNumberOrigin |
long : the origin (inclusive) of each random value |
randomNumberBound |
long : the bound (exclusive) of each random value |
Returns | |
---|---|
LongStream |
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 |
long : the number of values to generate |
randomNumberOrigin |
long : the origin (inclusive) of each random value |
randomNumberBound |
long : the bound (exclusive) of each random value |
Returns | |
---|---|
LongStream |
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 | |
---|---|
boolean |
a pseudorandom boolean value |
public double nextDouble ()
Returns a pseudorandom double
value between zero
(inclusive) and one (exclusive).
Returns | |
---|---|
double |
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 |
double : the upper bound (exclusive). Must be positive. |
Returns | |
---|---|
double |
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 |
double : the least value returned |
bound |
double : the upper bound (exclusive) |
Returns | |
---|---|
double |
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 | |
---|---|
float |
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 | |
---|---|
double |
the next pseudorandom, Gaussian ("normally") distributed
double value with mean 0.0 and
standard deviation 1.0 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 |
int : the least value returned |
bound |
int : the upper bound (exclusive) |
Returns | |
---|---|
int |
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 | |
---|---|
int |
a pseudorandom int value |
public int nextInt (int bound)
Returns a pseudorandom int
value between zero (inclusive)
and the specified bound (exclusive).
Parameters | |
---|---|
bound |
int : the upper bound (exclusive). Must be positive. |
Returns | |
---|---|
int |
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 |
long : the least value returned |
bound |
long : the upper bound (exclusive) |
Returns | |
---|---|
long |
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 |
long : the upper bound (exclusive). Must be positive. |
Returns | |
---|---|
long |
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 | |
---|---|
long |
a pseudorandom long value |
public void setSeed (long seed)
Throws UnsupportedOperationException
. Setting seeds in
this generator is not supported.
Parameters | |
---|---|
seed |
long : the initial seed |
Throws | |
---|---|
UnsupportedOperationException |
always |
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 |
int : random bits |
Returns | |
---|---|
int |
the next pseudorandom value from this random number generator's sequence |