Module java.base
Package java.util

Class 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 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

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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.
    • 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.
        Returns:
        a stream of pseudorandom int values
        Implementation Note:
        This method is implemented to be equivalent to ints(Long.MAX_VALUE).
      • 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).
        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
        Implementation Note:
        This method is implemented to be equivalent to ints(Long.MAX_VALUE, randomNumberOrigin, 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.
        Returns:
        a stream of pseudorandom long values
        Implementation Note:
        This method is implemented to be equivalent to longs(Long.MAX_VALUE).
      • 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).
        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
        Implementation Note:
        This method is implemented to be equivalent to longs(Long.MAX_VALUE, randomNumberOrigin, 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).
        Returns:
        a stream of pseudorandom double values
        Implementation Note:
        This method is implemented to be equivalent to doubles(Long.MAX_VALUE).
      • 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).
        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
        Implementation Note:
        This method is implemented to be equivalent to doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).