Class ThreadLocalRandom

java.lang.Object

java.util.Random

java.util.concurrent.ThreadLocalRandom

All Implemented Interfaces:

Serializable, RandomGenerator

public final class ThreadLocalRandom
extends Random

A random number generator (with period 2⁶⁴) 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 accidentally 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.

Since:

1.7

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces declared in interface RandomGenerator

RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator

Modifier and Type	Interface	Description
static interface	RandomGenerator.ArbitrarilyJumpableGenerator	This interface is designed to provide a common protocol for objects that generate sequences of pseudorandom values and can easily jump forward, by an arbitrary amount, to a distant point in the state cycle.
static interface	RandomGenerator.JumpableGenerator	This interface is designed to provide a common protocol for objects that generate pseudorandom values and can easily jump forward, by a moderate amount (ex. 264) to a distant point in the state cycle.
static interface	RandomGenerator.LeapableGenerator	This interface is designed to provide a common protocol for objects that generate sequences of pseudorandom values and can easily not only jump but also leap forward, by a large amount (ex. 2128), to a very distant point in the state cycle.
static interface	RandomGenerator.SplittableGenerator	This interface is designed to provide a common protocol for objects that generate sequences of pseudorandom values and can be split into two objects (the original one and a new one) each of which obey that same protocol (and therefore can be recursively split indefinitely).
static interface	RandomGenerator.StreamableGenerator	The RandomGenerator.StreamableGenerator interface augments the RandomGenerator interface to provide methods that return streams of RandomGenerator objects.

Method Summary

Modifier and Type	Method	Description
static ThreadLocalRandom	current()	Returns the current thread's ThreadLocalRandom object.
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 a pseudorandom number with the indicated number of low-order bits.
double	nextDouble(double bound)	Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).
double	nextDouble(double origin, double bound)	Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive).
float	nextFloat(float bound)	Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).
float	nextFloat(float origin, float bound)	Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive).
double	nextGaussian()	Returns a double value pseudorandomly chosen from a Gaussian (normal) distribution whose mean is 0 and whose standard deviation is 1.
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.
int	nextInt(int origin, int bound)	Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive).
long	nextLong(long bound)	Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).
long	nextLong(long origin, long bound)	Returns a pseudorandomly chosen long value between the specified origin (inclusive) and the specified bound (exclusive).
void	setSeed(long seed)	Throws UnsupportedOperationException.

Methods declared in class Random

from, nextBoolean, nextBytes, nextDouble, nextFloat, nextInt, nextLong

Modifier and Type	Method	Description
static Random	from(RandomGenerator generator)	Returns an instance of Random that delegates method calls to the RandomGenerator argument.
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.
int	nextInt()	Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.
long	nextLong()	Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.

Methods declared in class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Modifier and Type	Method	Description
protected Object	clone()	Creates and returns a copy of this object.
boolean	equals(Object obj)	Indicates whether some other object is "equal to" this one.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
final Class<?>	getClass()	Returns the runtime class of this Object.
int	hashCode()	Returns a hash code value for this 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()	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
final void	wait(long timeoutMillis)	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
final void	wait(long timeoutMillis, int nanos)	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Methods declared in interface RandomGenerator

equiDoubles, isDeprecated, nextExponential, nextGaussian

Modifier and Type	Method	Description
default DoubleStream	equiDoubles(double left, double right, boolean isLeftIncluded, boolean isRightIncluded)	Returns an effectively unlimited stream of pseudorandomly chosen double values, where each value is between the specified left boundary and the specified right boundary.
default boolean	isDeprecated()	Return true if the implementation of RandomGenerator (algorithm) has been marked for deprecation.
default double	nextExponential()	Returns a nonnegative double value pseudorandomly chosen from an exponential distribution whose mean is 1.
default double	nextGaussian(double mean, double stddev)	Returns a double value pseudorandomly chosen from a Gaussian (normal) distribution with a mean and standard deviation specified by the arguments.

Method Details

current

public static ThreadLocalRandom current()

Returns the current thread's ThreadLocalRandom object. Methods of this object should be called only by the current thread, not by other threads.

Returns:

the current thread's ThreadLocalRandom

setSeed

public void setSeed(long seed)

Throws UnsupportedOperationException. Setting seeds in this generator is not supported.

Overrides:

setSeed in class Random

Parameters:

seed - the seed value

Throws:

UnsupportedOperationException - always

next

protected int next(int bits)

Generates a pseudorandom number with the indicated number of low-order bits. Because this class has no subclasses, this method cannot be invoked or overridden.

Overrides:

next in class Random

Parameters:

bits - random bits

Returns:

the next pseudorandom value from this random number generator's sequence

nextInt

public 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. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.

Specified by:

nextInt in interface RandomGenerator

Overrides:

nextInt in class Random

Parameters:

bound - the upper bound (exclusive). Must be positive.

Returns:

the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

Throws:

IllegalArgumentException - if bound is not positive

nextInt

public int nextInt(int origin,
 int bound)

Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:

origin - the least value that can be returned

bound - the upper bound (exclusive) for the returned value

Returns:

a pseudorandomly chosen int value between the origin (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if origin is greater than or equal to bound

nextLong

public long nextLong(long bound)

Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).

Parameters:

bound - the upper bound (exclusive) for the returned value. Must be positive.

Returns:

a pseudorandomly chosen long value between zero (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if bound is not positive

nextLong

public long nextLong(long origin,
 long bound)

Returns a pseudorandomly chosen long value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:

origin - the least value that can be returned

bound - the upper bound (exclusive) for the returned value

Returns:

a pseudorandomly chosen long value between the origin (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if origin is greater than or equal to bound

nextGaussian

public double nextGaussian()

Returns a double value pseudorandomly chosen from a Gaussian (normal) distribution whose mean is 0 and whose standard deviation is 1.

Specified by:

nextGaussian in interface RandomGenerator

Overrides:

nextGaussian in class Random

Implementation Note:

This implementation invokes the default implementation of RandomGenerator.nextGaussian(), and so it uses McFarland's fast modified ziggurat algorithm rather than the polar method described in the superclass.

Returns:

a double value pseudorandomly chosen from a Gaussian distribution

nextFloat

public float nextFloat(float bound)

Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).

Parameters:

bound - the upper bound (exclusive) for the returned value. Must be positive and finite

Returns:

a pseudorandomly chosen float value between zero (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if bound is not both positive and finite

Since:

17

nextFloat

public float nextFloat(float origin,
 float bound)

Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:

origin - the least value that can be returned

bound - the upper bound (exclusive)

Returns:

a pseudorandomly chosen float value between the origin (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

Since:

17

nextDouble

public double nextDouble(double bound)

Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).

Parameters:

bound - the upper bound (exclusive) for the returned value. Must be positive and finite

Returns:

a pseudorandomly chosen double value between zero (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if bound is not both positive and finite

nextDouble

public double nextDouble(double origin,
 double bound)

Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:

origin - the least value that can be returned

bound - the upper bound (exclusive) for the returned value

Returns:

a pseudorandomly chosen double value between the origin (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

ints

public IntStream ints(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom int values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

ints

public IntStream ints()

Returns an effectively unlimited stream of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Implementation Note:

This method is implemented to be equivalent to ints(Long.MAX_VALUE).

Returns:

a stream of pseudorandom int values

Since:

1.8

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).

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

int nextInt(int origin, int bound) {
  int n = bound - origin;
  if (n > 0) {
    return nextInt(n) + origin;
  }
  else {  // range not representable as int
    int r;
    do {
      r = nextInt();
    } while (r < origin || r >= bound);
    return r;
  }
}

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

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

Since:

1.8

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).

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

int nextInt(int origin, int bound) {
  int n = bound - origin;
  if (n > 0) {
    return nextInt(n) + origin;
  }
  else {  // range not representable as int
    int r;
    do {
      r = nextInt();
    } while (r < origin || r >= bound);
    return r;
  }
}

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Implementation Note:

This method is implemented to be equivalent to ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

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

Since:

1.8

longs

public LongStream longs(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom long values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

longs

public LongStream longs()

Returns an effectively unlimited stream of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Implementation Note:

This method is implemented to be equivalent to longs(Long.MAX_VALUE).

Returns:

a stream of pseudorandom long values

Since:

1.8

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).

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

long nextLong(long origin, long bound) {
  long r = nextLong();
  long n = bound - origin, m = n - 1;
  if ((n & m) == 0L)  // power of two
    r = (r & m) + origin;
  else if (n > 0L) {  // reject over-represented candidates
    for (long u = r >>> 1;            // ensure nonnegative
         u + m - (r = u % n) < 0L;    // rejection check
         u = nextLong() >>> 1) // retry
        ;
    r += origin;
  }
  else {              // range not representable as long
    while (r < origin || r >= bound)
      r = nextLong();
  }
  return r;
}

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

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

Since:

1.8

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).

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

long nextLong(long origin, long bound) {
  long r = nextLong();
  long n = bound - origin, m = n - 1;
  if ((n & m) == 0L)  // power of two
    r = (r & m) + origin;
  else if (n > 0L) {  // reject over-represented candidates
    for (long u = r >>> 1;            // ensure nonnegative
         u + m - (r = u % n) < 0L;    // rejection check
         u = nextLong() >>> 1) // retry
        ;
    r += origin;
  }
  else {              // range not representable as long
    while (r < origin || r >= bound)
      r = nextLong();
  }
  return r;
}

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Implementation Note:

This method is implemented to be equivalent to longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

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

Since:

1.8

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).

A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Parameters:

streamSize - the number of values to generate

Returns:

a stream of double values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

doubles

public DoubleStream doubles()

Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).

A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Implementation Note:

This method is implemented to be equivalent to doubles(Long.MAX_VALUE).

Returns:

a stream of pseudorandom double values

Since:

1.8

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).

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

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, or randomNumberOrigin is not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8

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).

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Implementation Note:

This method is implemented to be equivalent to doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

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 not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8