java8.util.concurrent

Class ThreadLocalRandom

java.lang.Object

java.util.Random

java8.util.concurrent.ThreadLocalRandom

All Implemented Interfaces:

Serializable

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 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

Method Summary

Modifier and Type	Method and Description
static ThreadLocalRandom	current() Returns the current thread's ThreadLocalRandom.
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).
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() Returns a pseudorandom int value.
int	nextInt(int bound) Returns a pseudorandom int value between zero (inclusive) and the specified bound (exclusive).
int	nextInt(int origin, int bound) Returns a pseudorandom int value between the specified origin (inclusive) and the specified bound (exclusive).
long	nextLong() Returns a pseudorandom long value.
long	nextLong(long bound) Returns a pseudorandom long 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).
void	setSeed(long seed) Throws UnsupportedOperationException.

Methods inherited from class java.lang.Object

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

Method Detail

current

public static ThreadLocalRandom current()

Returns the current thread's ThreadLocalRandom.

Returns:

the current thread's ThreadLocalRandom

setSeed

public void setSeed(long seed)

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

Parameters:

seed - not supported

Throws:

UnsupportedOperationException - always

nextInt

public int nextInt()

Returns a pseudorandom int value.

Returns:

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

Returns:

a pseudorandom int value between zero (inclusive) and the bound (exclusive)

Throws:

IllegalArgumentException - if bound is not positive

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 - the least value returned

bound - the upper bound (exclusive)

Returns:

a pseudorandom 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()

Returns a pseudorandom long value.

Returns:

a pseudorandom long value

nextLong

public long nextLong(long bound)

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

Parameters:

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

Returns:

a pseudorandom 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 pseudorandom long value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:

origin - the least value returned

bound - the upper bound (exclusive)

Returns:

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

Throws:

IllegalArgumentException - if origin is greater than or equal to bound

nextDouble

public double nextDouble()

Returns a pseudorandom double value between zero (inclusive) and one (exclusive).

Returns:

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

Returns:

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

Throws:

IllegalArgumentException - if bound is not positive

nextDouble

public double nextDouble(double origin,
                         double bound)

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

Parameters:

origin - the least value returned

bound - the upper bound (exclusive)

Returns:

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

Throws:

IllegalArgumentException - if origin is greater than or equal to bound

nextBoolean

public boolean nextBoolean()

Returns a pseudorandom boolean value.

Returns:

a pseudorandom boolean value

nextFloat

public float nextFloat()

Returns a pseudorandom float value between zero (inclusive) and one (exclusive).

Returns:

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 ThreadLocalRandom as if by a thread-local 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:

the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence

ints

public IntStream ints(long streamSize)

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

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.

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

Overrides:

ints in class Random

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).

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).

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

Overrides:

ints in class Random

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.

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.

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

Overrides:

longs in class Random

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).

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).

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

Overrides:

longs in class Random

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).

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).

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

Overrides:

doubles in class Random

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).

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 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).

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

Overrides:

doubles in class Random

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 greater than or equal to randomNumberBound

Since:

1.8