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 accidently share a ThreadLocalRandom across multiple threads.

This class also provides additional commonly used bounded random generation methods.

Since:
1.7
Author:
Doug Lea
See Also:
Serialized Form

  • Method Summary

    Modifier and Type Method Description
    static ThreadLocalRandom current()
    Returns the current thread's ThreadLocalRandom.
    protected int next​(int bits)
    Returns a pseudo-random uniformly distributed int value of the number of bits specified by the argument bits as described by Donald E.
    double nextDouble​(double n)
    Returns a pseudorandom, uniformly distributed double value between 0 (inclusive) and the specified value (exclusive).
    double nextDouble​(double least, double bound)
    Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
    int nextInt​(int least, int bound)
    Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
    long nextLong​(long n)
    Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).
    long nextLong​(long least, long bound)
    Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
    void setSeed​(long seed)
    Throws UnsupportedOperationException.

    Methods inherited from class java.util.Random

    nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong

    Methods inherited from 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
      Throws:
      UnsupportedOperationException - always

    • next

      protected int next​(int bits)
      Description copied from class: Random
      Returns a pseudo-random uniformly distributed int value of the number of bits specified by the argument bits as described by Donald E. Knuth in The Art of Computer Programming, Volume 2: Seminumerical Algorithms, section 3.2.1.

      Most applications will want to use one of this class' convenience methods instead.

      Overrides:
      next in class Random

    • nextInt

      public int nextInt​(int least, int bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      Parameters:
      least - the least value returned
      bound - the upper bound (exclusive)
      Returns:
      the next value
      Throws:
      IllegalArgumentException - if least greater than or equal to bound

    • nextLong

      public long nextLong​(long n)
      Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).
      Parameters:
      n - the bound on the random number to be returned. Must be positive.
      Returns:
      the next value
      Throws:
      IllegalArgumentException - if n is not positive

    • nextLong

      public long nextLong​(long least, long bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      Parameters:
      least - the least value returned
      bound - the upper bound (exclusive)
      Returns:
      the next value
      Throws:
      IllegalArgumentException - if least greater than or equal to bound

    • nextDouble

      public double nextDouble​(double n)
      Returns a pseudorandom, uniformly distributed double value between 0 (inclusive) and the specified value (exclusive).
      Parameters:
      n - the bound on the random number to be returned. Must be positive.
      Returns:
      the next value
      Throws:
      IllegalArgumentException - if n is not positive

    • nextDouble

      public double nextDouble​(double least, double bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      Parameters:
      least - the least value returned
      bound - the upper bound (exclusive)
      Returns:
      the next value
      Throws:
      IllegalArgumentException - if least greater than or equal to bound