Module java.base
Package java.util.concurrent

Class ThreadLocalRandom

java.lang.Object
java.util.Random
java.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
See Also:
Serialized Form

  • Method Summary

    Modifier and Type Method 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 a pseudorandom number with the indicated number of low-order bits.
    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).
    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 declared in class java.util.Random

    nextBytes, nextGaussian

    Methods declared in class java.lang.Object

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

  • Method Details

    • 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)
      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()
      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)

    • 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
      Implementation Note:
      This method is implemented to be equivalent to ints(Long.MAX_VALUE).
      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
      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
      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
      Implementation Note:
      This method is implemented to be equivalent to longs(Long.MAX_VALUE).
      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
      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
      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
      Implementation Note:
      This method is implemented to be equivalent to doubles(Long.MAX_VALUE).
      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).
      Overrides:
      doubles in class Random
      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
      Since:
      1.8