java8.util

Class SplittableRandom

java.lang.Object

java8.util.SplittableRandom

public final class SplittableRandom
extends Object

A generator of uniform pseudorandom values applicable for use in (among other contexts) isolated parallel computations that may generate subtasks. Class SplittableRandom supports methods for producing pseudorandom numbers of type int, long, and double with similar usages as for class Random but differs in the following ways:

• Series of generated values pass the DieHarder suite testing independence and uniformity properties of random number generators. (Most recently validated with version 3.31.1.) These tests validate only the methods for certain types and ranges, but similar properties are expected to hold, at least approximately, for others as well. The period (length of any series of generated values before it repeats) is at least 2⁶⁴.
• Method split() constructs and returns a new SplittableRandom instance that shares no mutable state with the current instance. However, with very high probability, the values collectively generated by the two objects have the same statistical properties as if the same quantity of values were generated by a single thread using a single SplittableRandom object.
• Instances of SplittableRandom are not thread-safe. They are designed to be split, not shared, across threads. For example, a fork/join-style computation using random numbers might include a construction of the form new Subtask(aSplittableRandom.split()).fork().
• This class provides additional methods for generating random streams, that employ the above techniques when used in stream.parallel() mode.

Instances of SplittableRandom 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:

1.8

Author:

Guy Steele, Doug Lea

Constructor Summary

Constructors

Constructor and Description
SplittableRandom() Creates a new SplittableRandom instance that is likely to generate sequences of values that are statistically independent of those of any other instances in the current program; and may, and typically does, vary across program invocations.
SplittableRandom(long seed) Creates a new SplittableRandom instance using the specified initial seed.

Method Summary

Modifier and Type	Method and Description
DoubleStream	doubles() Returns an effectively unlimited stream of pseudorandom double values from this generator and/or one split from it; each value is between zero (inclusive) and one (exclusive).
DoubleStream	doubles(double randomNumberOrigin, double randomNumberBound) Returns an effectively unlimited stream of pseudorandom double values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).
DoubleStream	doubles(long streamSize) Returns a stream producing the given streamSize number of pseudorandom double values from this generator and/or one split from it; each value is 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 from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).
IntStream	ints() Returns an effectively unlimited stream of pseudorandom int values from this generator and/or one split from it.
IntStream	ints(int randomNumberOrigin, int randomNumberBound) Returns an effectively unlimited stream of pseudorandom int values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).
IntStream	ints(long streamSize) Returns a stream producing the given streamSize number of pseudorandom int values from this generator and/or one split from it.
IntStream	ints(long streamSize, int randomNumberOrigin, int randomNumberBound) Returns a stream producing the given streamSize number of pseudorandom int values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).
LongStream	longs() Returns an effectively unlimited stream of pseudorandom long values from this generator and/or one split from it.
LongStream	longs(long streamSize) Returns a stream producing the given streamSize number of pseudorandom long values from this generator and/or one split from it.
LongStream	longs(long randomNumberOrigin, long randomNumberBound) Returns an effectively unlimited stream of pseudorandom long values from this generator and/or one split from it; each value conforms 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 values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).
boolean	nextBoolean() Returns a pseudorandom boolean value.
void	nextBytes(byte[] bytes) Fills a user-supplied byte array with generated pseudorandom bytes.
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).
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).
SplittableRandom	split() Constructs and returns a new SplittableRandom instance that shares no mutable state with this instance.

Methods inherited from class java.lang.Object

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

Constructor Detail

SplittableRandom

public SplittableRandom(long seed)

Creates a new SplittableRandom instance using the specified initial seed. SplittableRandom instances created with the same seed in the same program generate identical sequences of values.

Parameters:

seed - the initial seed

SplittableRandom

public SplittableRandom()

Creates a new SplittableRandom instance that is likely to generate sequences of values that are statistically independent of those of any other instances in the current program; and may, and typically does, vary across program invocations.

Method Detail

split

public SplittableRandom split()

Constructs and returns a new SplittableRandom instance that shares no mutable state with this instance. However, with very high probability, the set of values collectively generated by the two objects has the same statistical properties as if the same quantity of values were generated by a single thread using a single SplittableRandom object. Either or both of the two objects may be further split using the split() method, and the same expected statistical properties apply to the entire set of generators constructed by such recursive splitting.

Returns:

the new SplittableRandom instance

nextBytes

public void nextBytes(byte[] bytes)

Fills a user-supplied byte array with generated pseudorandom bytes.

Parameters:

bytes - the byte array to fill with pseudorandom bytes

Throws:

NullPointerException - if bytes is null

Since:

10

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

ints

public IntStream ints(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom int values from this generator and/or one split from it.

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom int values

Throws:

IllegalArgumentException - if streamSize is less than zero

ints

public IntStream ints()

Returns an effectively unlimited stream of pseudorandom int values from this generator and/or one split from it.

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

Returns:

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 from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).

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

ints

public IntStream ints(int randomNumberOrigin,
                      int randomNumberBound)

Returns an effectively unlimited stream of pseudorandom int values from this generator and/or one split from it; each value conforms 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 - 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

longs

public LongStream longs(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom long values from this generator and/or one split from it.

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom long values

Throws:

IllegalArgumentException - if streamSize is less than zero

longs

public LongStream longs()

Returns an effectively unlimited stream of pseudorandom long values from this generator and/or one split from it.

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

Returns:

a stream of pseudorandom long values

longs

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

Returns a stream producing the given streamSize number of pseudorandom long values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).

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

longs

public LongStream longs(long randomNumberOrigin,
                        long randomNumberBound)

Returns an effectively unlimited stream of pseudorandom long values from this generator and/or one split from it; each value conforms 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 - 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

doubles

public DoubleStream doubles(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom double values from this generator and/or one split from it; each value is between zero (inclusive) and one (exclusive).

Parameters:

streamSize - the number of values to generate

Returns:

a stream of double values

Throws:

IllegalArgumentException - if streamSize is less than zero

doubles

public DoubleStream doubles()

Returns an effectively unlimited stream of pseudorandom double values from this generator and/or one split from it; each value is between zero (inclusive) and one (exclusive).

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

Returns:

a stream of pseudorandom double values

doubles

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

Returns a stream producing the given streamSize number of pseudorandom double values from this generator and/or one split from it; each value conforms to the given origin (inclusive) and bound (exclusive).

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

doubles

public DoubleStream doubles(double randomNumberOrigin,
                            double randomNumberBound)

Returns an effectively unlimited stream of pseudorandom double values from this generator and/or one split from it; each value conforms 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 - 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