ThreadLocalRandom
public
class
ThreadLocalRandom
extends Random
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 property
java.util.secureRandomSeed is set to true.
Summary
Public methods |
|---|
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 methods |
|---|
int
|
next(int bits)
Generates the next pseudorandom number.
|
Inherited methods |
|---|
 From
class
java.util.Random
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).
|
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(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).
|
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.
|
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).
|
int
|
next(int bits)
Generates the next pseudorandom number.
|
boolean
|
nextBoolean()
Returns the next pseudorandom, uniformly distributed
boolean value from this random number generator's
sequence.
|
void
|
nextBytes(byte[] bytes)
Generates random bytes and places them into a user-supplied
byte array.
|
double
|
nextDouble()
Returns the next pseudorandom, uniformly distributed
double value between 0.0 and
1.0 from this random number generator's sequence.
|
float
|
nextFloat()
Returns the next pseudorandom, uniformly distributed float
value between 0.0 and 1.0 from this random
number generator's sequence.
|
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 the next pseudorandom, uniformly distributed int
value from this random number generator's sequence.
|
int
|
nextInt(int n)
Returns a pseudorandom, uniformly distributed int value
between 0 (inclusive) and the specified value (exclusive), drawn from
this random number generator's sequence.
|
long
|
nextLong()
Returns the next pseudorandom, uniformly distributed long
value from this random number generator's sequence.
|
void
|
setSeed(long seed)
Sets the seed of this random number generator using a single
long seed.
|
|
From
class
java.lang.Object
Object
|
clone()
Creates and returns a copy of this object.
|
boolean
|
equals(Object obj)
Indicates whether some other object is "equal to" this one.
|
void
|
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
final
Class<?>
|
getClass()
Returns the runtime class of this Object.
|
int
|
hashCode()
Returns a hash code value for the object.
|
final
void
|
notify()
Wakes up a single thread that is waiting on this object's
monitor.
|
final
void
|
notifyAll()
Wakes up all threads that are waiting on this object's monitor.
|
String
|
toString()
Returns a string representation of the object.
|
final
void
|
wait(long millis, int nanos)
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object, or
some other thread interrupts the current thread, or a certain
amount of real time has elapsed.
|
final
void
|
wait(long millis)
Causes the current thread to wait until either another thread invokes the
notify() method or the
notifyAll() method for this object, or a
specified amount of time has elapsed.
|
final
void
|
wait()
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object.
|
|
Public methods
doubles
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) |
doubles
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 |
doubles
DoubleStream doubles ()
Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one
(exclusive).
Implementation Note:
- This method is implemented to be equivalent to
doubles(Long.MAX_VALUE).
doubles
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).
Implementation Note:
- This method is implemented to be equivalent to
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) |
ints
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 |
ints
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).
Implementation Note:
- This method is implemented to be equivalent to
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) |
ints
IntStream ints ()
Returns an effectively unlimited stream of pseudorandom int
values.
Implementation Note:
- This method is implemented to be equivalent to
ints(Long.MAX_VALUE).
| Returns |
|---|
IntStream |
a stream of pseudorandom int values |
ints
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 |
longs
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 |
longs
LongStream longs ()
Returns an effectively unlimited stream of pseudorandom long
values.
Implementation Note:
- This method is implemented to be equivalent to
longs(Long.MAX_VALUE).
| Returns |
|---|
LongStream |
a stream of pseudorandom long values |
longs
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).
Implementation Note:
- This method is implemented to be equivalent to
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) |
longs
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 |
nextBoolean
boolean nextBoolean ()
Returns a pseudorandom boolean value.
| Returns |
|---|
boolean |
a pseudorandom boolean value
|
nextDouble
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)
|
nextDouble
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) |
nextDouble
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) |
nextFloat
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)
|
nextGaussian
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
|
nextInt
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) |
nextInt
int nextInt ()
Returns a pseudorandom int value.
| Returns |
|---|
int |
a pseudorandom int value
|
nextInt
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) |
nextLong
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) |
nextLong
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) |
nextLong
long nextLong ()
Returns a pseudorandom long value.
| Returns |
|---|
long |
a pseudorandom long value
|
setSeed
void setSeed (long seed)
Throws UnsupportedOperationException. Setting seeds in
this generator is not supported.
| Parameters |
|---|
seed |
long:
the initial seed
|
Protected methods
next
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 |
Developers