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

Methods

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.

Methods inherited from class java.util.Random

nextBytes

Methods inherited from class java.lang.Object

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

Methods

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
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
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
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

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