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ThreadLocalRandom

public class ThreadLocalRandom
extends Random

java.lang.Object
↳	java.util.Random
	↳	java.util.concurrent.ThreadLocalRandom

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#getProperty java.util.secureRandomSeed is set to true.

Summary

Public methods
`static ThreadLocalRandom`	`current()` Returns the current thread's `ThreadLocalRandom`.
`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).
`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()` 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).
`IntStream`	`ints(long streamSize)` Returns a stream producing the given `streamSize` number 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()` Returns an effectively unlimited stream 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(long streamSize)` Returns a stream producing the given `streamSize` number of pseudorandom `long` values.
`LongStream`	`longs()` Returns an effectively unlimited stream 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).
`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(int origin, int bound)` Returns a pseudorandom `int` value between the specified origin (inclusive) and the specified bound (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).
`long`	`nextLong(long origin, long bound)` Returns a pseudorandom `long` value between the specified origin (inclusive) and the specified bound (exclusive).
`long`	`nextLong(long bound)` Returns a pseudorandom `long` value between zero (inclusive) and the specified bound (exclusive).
`long`	`nextLong()` Returns a pseudorandom `long` value.
`void`	`setSeed(long seed)` Throws `UnsupportedOperationException`.

Protected methods
`int`	`next(int bits)` Generates the next pseudorandom number.

Inherited methods

From class


        
          java.util.Random

`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()` 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, 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(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).
`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()` Returns an effectively unlimited stream of pseudorandom `int` values.
`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).
`int`	`next(int bits)` Generates the next pseudorandom number.
`boolean`	`nextBoolean()` Returns the next pseudorandom, uniformly distributed `boolean` value from this random number generator's sequence.
`void`	`nextBytes(byte[] bytes)` Generates random bytes and places them into a user-supplied byte array.
`double`	`nextDouble()` Returns the next pseudorandom, uniformly distributed `double` value between `0.0` and `1.0` from this random number generator's sequence.
`float`	`nextFloat()` Returns the next pseudorandom, uniformly distributed `float` value between `0.0` and `1.0` from this random number generator's sequence.
`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 the next pseudorandom, uniformly distributed `int` value from this random number generator's sequence.
`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.
`long`	`nextLong()` Returns the next pseudorandom, uniformly distributed `long` value from this random number generator's sequence.
`void`	`setSeed(long seed)` Sets the seed of this random number generator using a single `long` seed.

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

Public methods

current

public static ThreadLocalRandom current ()

Returns the current thread's ThreadLocalRandom.

Returns
`ThreadLocalRandom`	the current thread's `ThreadLocalRandom`

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).

Parameters
`streamSize`	`long`: the number of values to generate
`randomNumberOrigin`	`double`: the origin (inclusive) of each random value
`randomNumberBound`	`double`: the bound (exclusive) of each random value

Returns
`DoubleStream`	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`

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).

Parameters
`streamSize`	`long`: the number of values to generate

Returns
`DoubleStream`	a stream of `double` values

Throws
`IllegalArgumentException`	if `streamSize` is less than zero

doubles

public DoubleStream doubles ()

Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).

Implementation Note:

This method is implemented to be equivalent to doubles(Long.MAX_VALUE).

Returns
`DoubleStream`	a stream of pseudorandom `double` values

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).

Implementation Note:

This method is implemented to be equivalent to doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

Parameters
`randomNumberOrigin`	`double`: the origin (inclusive) of each random value
`randomNumberBound`	`double`: the bound (exclusive) of each random value

Returns
`DoubleStream`	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`

ints

public IntStream ints (long streamSize)

Returns a stream producing the given streamSize number of pseudorandom int values.

Parameters
`streamSize`	`long`: the number of values to generate

Returns
`IntStream`	a stream of pseudorandom `int` values

Throws
`IllegalArgumentException`	if `streamSize` is less than zero

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).

Implementation Note:

This method is implemented to be equivalent to ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

Parameters
`randomNumberOrigin`	`int`: the origin (inclusive) of each random value
`randomNumberBound`	`int`: the bound (exclusive) of each random value

Returns
`IntStream`	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`

ints

public IntStream ints ()

Returns an effectively unlimited stream of pseudorandom int values.

Implementation Note:

This method is implemented to be equivalent to ints(Long.MAX_VALUE).

Returns
`IntStream`	a stream of pseudorandom `int` values

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).

Parameters
`streamSize`	`long`: the number of values to generate
`randomNumberOrigin`	`int`: the origin (inclusive) of each random value
`randomNumberBound`	`int`: the bound (exclusive) of each random value

Returns
`IntStream`	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`

longs

public LongStream longs (long streamSize)

Returns a stream producing the given streamSize number of pseudorandom long values.

Parameters
`streamSize`	`long`: the number of values to generate

Returns
`LongStream`	a stream of pseudorandom `long` values

Throws
`IllegalArgumentException`	if `streamSize` is less than zero

longs

public LongStream longs ()

Returns an effectively unlimited stream of pseudorandom long values.

Implementation Note:

This method is implemented to be equivalent to longs(Long.MAX_VALUE).

Returns
`LongStream`	a stream of pseudorandom `long` values

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).

Implementation Note:

This method is implemented to be equivalent to longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

Parameters
`randomNumberOrigin`	`long`: the origin (inclusive) of each random value
`randomNumberBound`	`long`: the bound (exclusive) of each random value

Returns
`LongStream`	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`

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).

Parameters
`streamSize`	`long`: the number of values to generate
`randomNumberOrigin`	`long`: the origin (inclusive) of each random value
`randomNumberBound`	`long`: the bound (exclusive) of each random value

Returns
`LongStream`	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`

nextBoolean

public boolean nextBoolean ()

Returns a pseudorandom boolean value.

Returns
`boolean`	a pseudorandom `boolean` value

nextDouble

public double nextDouble ()

Returns a pseudorandom double value between zero (inclusive) and one (exclusive).

Returns
`double`	a pseudorandom `double` value between zero (inclusive) and one (exclusive)

nextDouble

public double nextDouble (double bound)

Returns a pseudorandom double value between 0.0 (inclusive) and the specified bound (exclusive).

Parameters
`bound`	`double`: the upper bound (exclusive). Must be positive.

Returns
`double`	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`	`double`: the least value returned
`bound`	`double`: the upper bound (exclusive)

Returns
`double`	a pseudorandom `double` value between the origin (inclusive) and the bound (exclusive)

Throws
`IllegalArgumentException`	if `origin` is greater than or equal to `bound`

nextFloat

public float nextFloat ()

Returns a pseudorandom float value between zero (inclusive) and one (exclusive).

Returns
`float`	a pseudorandom `float` value between zero (inclusive) and one (exclusive)

nextGaussian

public 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.

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.

Returns
`double`	the next pseudorandom, Gaussian ("normally") distributed `double` value with mean `0.0` and standard deviation `1.0` from this random number generator's sequence

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`	`int`: the least value returned
`bound`	`int`: the upper bound (exclusive)

Returns
`int`	a pseudorandom `int` value between the origin (inclusive) and the bound (exclusive)

Throws
`IllegalArgumentException`	if `origin` is greater than or equal to `bound`

nextInt

public int nextInt ()

Returns a pseudorandom int value.

Returns
`int`	a pseudorandom `int` value

nextInt

public int nextInt (int bound)

Returns a pseudorandom int value between zero (inclusive) and the specified bound (exclusive).

Parameters
`bound`	`int`: the upper bound (exclusive). Must be positive.

Returns
`int`	a pseudorandom `int` 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`	`long`: the least value returned
`bound`	`long`: the upper bound (exclusive)

Returns
`long`	a pseudorandom `long` 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 pseudorandom long value between zero (inclusive) and the specified bound (exclusive).

Parameters
`bound`	`long`: the upper bound (exclusive). Must be positive.

Returns
`long`	a pseudorandom `long` value between zero (inclusive) and the bound (exclusive)

Throws
`IllegalArgumentException`	if `bound` is not positive

nextLong

public long nextLong ()

Returns a pseudorandom long value.

Returns
`long`	a pseudorandom `long` value

setSeed

public void setSeed (long seed)

Throws UnsupportedOperationException. Setting seeds in this generator is not supported.

Parameters
`seed`	`long`: the initial seed

Throws
`UnsupportedOperationException`	always

Protected methods

protected int next (int bits)

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.

Parameters
`bits`	`int`: random bits

Returns
`int`	the next pseudorandom value from this random number generator's sequence