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 securitysensitive applications. Additionally,
defaultconstructed 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 usersupplied
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 bound)
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
current
public static ThreadLocalRandom current ()
Returns the current thread's ThreadLocalRandom
.
doubles
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) 
doubles
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 
doubles
public 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
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).
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
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 
ints
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).
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
public 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
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 
longs
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 
longs
public 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
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).
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
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 
nextBoolean
public boolean nextBoolean ()
Returns a pseudorandom boolean
value.
Returns 
boolean 
a pseudorandom boolean value

nextDouble
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)

nextDouble
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) 
nextDouble
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) 
nextFloat
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)

nextGaussian
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

nextInt
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) 
nextInt
public int nextInt ()
Returns a pseudorandom int
value.
Returns 
int 
a pseudorandom int value

nextInt
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) 
nextLong
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) 
nextLong
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) 
nextLong
public long nextLong ()
Returns a pseudorandom long
value.
Returns 
long 
a pseudorandom long value

setSeed
public void setSeed (long seed)
Throws UnsupportedOperationException
. Setting seeds in
this generator is not supported.
Parameters 
seed 
long : the initial seed

Protected methods
next
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 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.
Parameters 
bits 
int : random bits 
Returns 
int 
the next pseudorandom value from this random number
generator's sequence 