Module java.base

Package java.util.concurrent

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

Author:

Doug Lea

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces declared in interface java.util.random.RandomGenerator

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

Method Summary

Modifier and Type	Method	Description
static ThreadLocalRandom	current()	Returns the current thread's ThreadLocalRandom object.
DoubleStream	doubles()
DoubleStream	doubles(double randomNumberOrigin, double randomNumberBound)
DoubleStream	doubles(long streamSize)
DoubleStream	doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)
IntStream	ints()
IntStream	ints(int randomNumberOrigin, int randomNumberBound)
IntStream	ints(long streamSize)
IntStream	ints(long streamSize, int randomNumberOrigin, int randomNumberBound)
LongStream	longs()
LongStream	longs(long streamSize)
LongStream	longs(long randomNumberOrigin, long randomNumberBound)
LongStream	longs(long streamSize, long randomNumberOrigin, long randomNumberBound)
protected int	next(int bits)	Generates a pseudorandom number with the indicated number of low-order bits.
double	nextDouble(double bound)
double	nextDouble(double origin, double bound)
float	nextFloat(float bound)
float	nextFloat(float origin, float bound)
int	nextInt(int bound)
int	nextInt(int origin, int bound)
long	nextLong(long bound)
long	nextLong(long origin, long bound)
void	setSeed(long seed)	Throws UnsupportedOperationException.

Methods declared in class java.util.Random

nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextLong

Methods declared in class java.lang.Object

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

Methods declared in interface java.util.random.RandomGenerator

isDeprecated, nextExponential, nextGaussian

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

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)

Specified by:

nextInt in interface RandomGenerator

Overrides:

nextInt in class Random

Throws:

IllegalArgumentException

nextInt

public int nextInt(int origin,
 int bound)

Throws:

IllegalArgumentException

nextLong

public long nextLong(long bound)

Throws:

IllegalArgumentException

nextLong

public long nextLong(long origin,
 long bound)

Throws:

IllegalArgumentException

nextFloat

public float nextFloat(float bound)

Throws:

IllegalArgumentException

Implementation Note:

nextFloat

public float nextFloat(float origin,
 float bound)

Throws:

IllegalArgumentException

Implementation Note:

nextDouble

public double nextDouble(double bound)

Throws:

IllegalArgumentException

Implementation Note:

nextDouble

public double nextDouble(double origin,
 double bound)

Throws:

IllegalArgumentException

Implementation Note:

ints

public IntStream ints(long streamSize)

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Throws:

IllegalArgumentException

Since:

1.8

ints

public IntStream ints()

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Since:

1.8

Implementation Note:

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

ints

public IntStream ints(long streamSize,
 int randomNumberOrigin,
 int randomNumberBound)

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Throws:

IllegalArgumentException

Since:

1.8

ints

public IntStream ints(int randomNumberOrigin,
 int randomNumberBound)

Specified by:

ints in interface RandomGenerator

Overrides:

ints in class Random

Throws:

IllegalArgumentException

Since:

1.8

Implementation Note:

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

longs

public LongStream longs(long streamSize)

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Throws:

IllegalArgumentException

Since:

1.8

longs

public LongStream longs()

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Since:

1.8

Implementation Note:

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

longs

public LongStream longs(long streamSize,
 long randomNumberOrigin,
 long randomNumberBound)

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Throws:

IllegalArgumentException

Since:

1.8

longs

public LongStream longs(long randomNumberOrigin,
 long randomNumberBound)

Specified by:

longs in interface RandomGenerator

Overrides:

longs in class Random

Throws:

IllegalArgumentException

Since:

1.8

Implementation Note:

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

doubles

public DoubleStream doubles(long streamSize)

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Throws:

IllegalArgumentException

Since:

1.8

doubles

public DoubleStream doubles()

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Since:

1.8

Implementation Note:

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

doubles

public DoubleStream doubles(long streamSize,
 double randomNumberOrigin,
 double randomNumberBound)

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Throws:

IllegalArgumentException

Since:

1.8

doubles

public DoubleStream doubles(double randomNumberOrigin,
 double randomNumberBound)

Specified by:

doubles in interface RandomGenerator

Overrides:

doubles in class Random

Throws:

IllegalArgumentException

Since:

1.8

Implementation Note:

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