Module java.base
Package java.util.concurrent

Class ThreadLocalRandom

java.lang.Object
java.util.Random
java.util.concurrent.ThreadLocalRandom
All Implemented Interfaces:
Serializable, RandomGenerator
public class ThreadLocalRandom extends Random
A random number generator (with period 264) 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:

  • Nested Class Summary

    Nested classes/interfaces declared in interface java.util.random.RandomGenerator

    RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator

  • Method Summary

    Modifier and Type
    Method
    Description
    static ThreadLocalRandom
    current()
    Returns the current thread's ThreadLocalRandom object.
    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.
    double
    nextDouble(double bound)
    Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).
    double
    nextDouble(double origin, double bound)
    Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive).
    float
    nextFloat(float bound)
    Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).
    float
    nextFloat(float origin, float bound)
    Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive).
    int
    nextInt(int bound)
    Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
    int
    nextInt(int origin, int bound)
    Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive).
    long
    nextLong(long bound)
    Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).
    long
    nextLong(long origin, long bound)
    Returns a pseudorandomly chosen 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

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

    Methods declared in class java.lang.Object

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

    Methods declared in interface java.util.random.RandomGenerator

    isDeprecated, nextExponential, nextGaussian

  • Method Details

    • current

      public static ThreadLocalRandom current()
      Returns the current thread's ThreadLocalRandom object. Methods of this object should be called only by the current thread, not by other threads.
      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(int bound)
      Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class Random
      Parameters:
      bound - the upper bound (exclusive). Must be positive.
      Returns:
      the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence
      Throws:
      IllegalArgumentException - if bound is not positive

    • nextInt

      public int nextInt(int origin, int bound)
      Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive).
      Parameters:
      origin - the least value that can be returned
      bound - the upper bound (exclusive) for the returned value
      Returns:
      a pseudorandomly chosen 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(long bound)
      Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).
      Parameters:
      bound - the upper bound (exclusive) for the returned value. Must be positive.
      Returns:
      a pseudorandomly chosen 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 pseudorandomly chosen long value between the specified origin (inclusive) and the specified bound (exclusive).
      Parameters:
      origin - the least value that can be returned
      bound - the upper bound (exclusive) for the returned value
      Returns:
      a pseudorandomly chosen long value between the origin (inclusive) and the bound (exclusive)
      Throws:
      IllegalArgumentException - if origin is greater than or equal to bound

    • nextFloat

      public float nextFloat(float bound)
      Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).
      Implementation Note:
      Parameters:
      bound - the upper bound (exclusive) for the returned value. Must be positive and finite
      Returns:
      a pseudorandomly chosen float value between zero (inclusive) and the bound (exclusive)
      Throws:
      IllegalArgumentException - if bound is not both positive and finite

    • nextFloat

      public float nextFloat(float origin, float bound)
      Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive).
      Implementation Note:
      Parameters:
      origin - the least value that can be returned
      bound - the upper bound (exclusive)
      Returns:
      a pseudorandomly chosen float value between the origin (inclusive) and the bound (exclusive)
      Throws:
      IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

    • nextDouble

      public double nextDouble(double bound)
      Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).
      Implementation Note:
      Parameters:
      bound - the upper bound (exclusive) for the returned value. Must be positive and finite
      Returns:
      a pseudorandomly chosen double value between zero (inclusive) and the bound (exclusive)
      Throws:
      IllegalArgumentException - if bound is not both positive and finite

    • nextDouble

      public double nextDouble(double origin, double bound)
      Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive).
      Implementation Note:
      Parameters:
      origin - the least value that can be returned
      bound - the upper bound (exclusive) for the returned value
      Returns:
      a pseudorandomly chosen double value between the origin (inclusive) and the bound (exclusive)
      Throws:
      IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

    • ints

      public IntStream ints(long streamSize)
      Returns a stream producing the given streamSize number of pseudorandom int values.

      A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

      Specified by:
      ints in interface RandomGenerator
      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.

      A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

      Specified by:
      ints in interface RandomGenerator
      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).

      A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound: 

       
 int nextInt(int origin, int bound) {
   int n = bound - origin;
   if (n > 0) {
     return nextInt(n) + origin;
   }
   else {  // range not representable as int
     int r;
     do {
       r = nextInt();
     } while (r < origin || r >= bound);
     return r;
   }
 }
      Specified by:
      ints in interface RandomGenerator
      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).

      A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound: 

       
 int nextInt(int origin, int bound) {
   int n = bound - origin;
   if (n > 0) {
     return nextInt(n) + origin;
   }
   else {  // range not representable as int
     int r;
     do {
       r = nextInt();
     } while (r < origin || r >= bound);
     return r;
   }
 }
      Specified by:
      ints in interface RandomGenerator
      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.

      A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

      Specified by:
      longs in interface RandomGenerator
      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.

      A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

      Specified by:
      longs in interface RandomGenerator
      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).

      A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound: 

       
 long nextLong(long origin, long bound) {
   long r = nextLong();
   long n = bound - origin, m = n - 1;
   if ((n & m) == 0L)  // power of two
     r = (r & m) + origin;
   else if (n > 0L) {  // reject over-represented candidates
     for (long u = r >>> 1;            // ensure nonnegative
          u + m - (r = u % n) < 0L;    // rejection check
          u = nextLong() >>> 1) // retry
         ;
     r += origin;
   }
   else {              // range not representable as long
     while (r < origin || r >= bound)
       r = nextLong();
   }
   return r;
 }
      Specified by:
      longs in interface RandomGenerator
      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).

      A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound: 

       
 long nextLong(long origin, long bound) {
   long r = nextLong();
   long n = bound - origin, m = n - 1;
   if ((n & m) == 0L)  // power of two
     r = (r & m) + origin;
   else if (n > 0L) {  // reject over-represented candidates
     for (long u = r >>> 1;            // ensure nonnegative
          u + m - (r = u % n) < 0L;    // rejection check
          u = nextLong() >>> 1) // retry
         ;
     r += origin;
   }
   else {              // range not representable as long
     while (r < origin || r >= bound)
       r = nextLong();
   }
   return r;
 }
      Specified by:
      longs in interface RandomGenerator
      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).

      A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

      Specified by:
      doubles in interface RandomGenerator
      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).

      A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

      Specified by:
      doubles in interface RandomGenerator
      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).

      A pseudorandom double value is generated as if it's the result of calling the following method with the origin and bound: 

       
 double nextDouble(double origin, double bound) {
   double r = nextDouble();
   r = r * (bound - origin) + origin;
   if (r >= bound) // correct for rounding
     r = Math.nextDown(bound);
   return r;
 }
      Specified by:
      doubles in interface RandomGenerator
      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 not finite, or randomNumberBound is not finite, 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).

      A pseudorandom double value is generated as if it's the result of calling the following method with the origin and bound: 

       
 double nextDouble(double origin, double bound) {
   double r = nextDouble();
   r = r * (bound - origin) + origin;
   if (r >= bound) // correct for rounding
     r = Math.nextDown(bound);
   return r;
 }
      Specified by:
      doubles in interface RandomGenerator
      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