java.util.concurrent

Class 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 accidently 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

    • 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).
      protected int next(int bits)
      Generates the next pseudorandom number.
      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.

    • 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.
        Overrides:
        setSeed in class  Random
        Parameters:
        seed - the initial seed
        Throws:
        UnsupportedOperationException - always

      • next

        protected int next(int bits)
        Description copied from class: Random
        Generates the next pseudorandom number. Subclasses should override this, as this is used by all other methods.

        The general contract of next is that it returns an int value and if the argument bits is between 1 and 32 (inclusive), then that many low-order bits of the returned value will be (approximately) independently chosen bit values, each of which is (approximately) equally likely to be 0 or 1. The method next is implemented by class Random by atomically updating the seed to 

         (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)
        and returning 
         (int)(seed >>> (48 - bits)).
        This is a linear congruential pseudorandom number generator, as defined by D. H. Lehmer and described by Donald E. Knuth in The Art of Computer Programming, Volume 3: Seminumerical Algorithms, section 3.2.1.
        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()
        Returns a pseudorandom int value.
        Overrides:
        nextInt in class  Random
        Returns:
        a pseudorandom int value

      • nextInt

        public int nextInt(int bound)
        Returns a pseudorandom int value between zero (inclusive) and the specified bound (exclusive).
        Overrides:
        nextInt in class  Random
        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.
        Overrides:
        nextLong in class  Random
        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).
        Overrides:
        nextDouble in class  Random
        Returns:
        a pseudorandom double value between zero (inclusive) and one (exclusive)
        See Also:
        Math.random()

      • 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.
        Overrides:
        nextBoolean in class  Random
        Returns:
        a pseudorandom boolean value

      • nextFloat

        public float nextFloat()
        Returns a pseudorandom float value between zero (inclusive) and one (exclusive).
        Overrides:
        nextFloat in class  Random
        Returns:
        a pseudorandom float value between zero (inclusive) and one (exclusive)

      • nextGaussian

        public double nextGaussian()
        Description copied from class: Random
        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 Random as if by a threadsafe 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.
        Overrides:
        nextGaussian in class  Random
        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.
        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).
        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.
        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).
        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).
        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
        IllegalArgumentException - if 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).
        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