ThreadLocalRandom
public final 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
.
Summary
Public methods |
static ThreadLocalRandom | current() Returns the current thread's ThreadLocalRandom object. |
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 the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence. |
double | nextDouble() Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence. |
double | nextDouble(double bound) |
double | nextDouble(double origin, double bound) |
float | nextFloat(float origin, float bound) |
float | nextFloat() Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence. |
float | nextFloat(float bound) |
int | nextInt(int origin, int bound) |
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(long origin, long bound) |
long | nextLong(long bound) |
long | nextLong() Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence. |
void | setSeed(long seed) Throws UnsupportedOperationException . |
Protected methods |
int | next(int bits) Generates a pseudorandom number with the indicated number of low-order bits. |
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). | static Random | from(RandomGenerator generator) Returns an instance of Random that delegates method calls to the RandomGenerator argument. | 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(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() 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 or updates the seed of this random number generator using the provided long seed value (optional operation). | |
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 timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. | final void | wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. | final void | wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted. | |
From interface java.util.random.RandomGenerator default DoubleStream | doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) Returns a stream producing the given streamSize number of pseudorandomly chosen double values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | default DoubleStream | doubles(long streamSize) Returns a stream producing the given streamSize number of pseudorandomly chosen double values. | default DoubleStream | doubles() Returns an effectively unlimited stream of pseudorandomly chosen double values. | default DoubleStream | doubles(double randomNumberOrigin, double randomNumberBound) Returns an effectively unlimited stream of pseudorandomly chosen double values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | static RandomGenerator | getDefault() Returns a RandomGenerator meeting the minimal requirement of having an algorithm whose state bits are greater than or equal 64. | default IntStream | ints(long streamSize) Returns a stream producing the given streamSize number of pseudorandomly chosen int values. | default IntStream | ints(int randomNumberOrigin, int randomNumberBound) Returns an effectively unlimited stream of pseudorandomly chosen int values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | default IntStream | ints() Returns an effectively unlimited stream of pseudorandomly chosen int values. | default IntStream | ints(long streamSize, int randomNumberOrigin, int randomNumberBound) Returns a stream producing the given streamSize number of pseudorandomly chosen int values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | default boolean | isDeprecated() Return true if the implementation of RandomGenerator (algorithm) has been marked for deprecation. | default LongStream | longs(long streamSize) Returns a stream producing the given streamSize number of pseudorandomly chosen long values. | default LongStream | longs() Returns an effectively unlimited stream of pseudorandomly chosen long values. | default LongStream | longs(long randomNumberOrigin, long randomNumberBound) Returns an effectively unlimited stream of pseudorandomly chosen long values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | default LongStream | longs(long streamSize, long randomNumberOrigin, long randomNumberBound) Returns a stream producing the given streamSize number of pseudorandomly chosen long values, where each value is between the specified origin (inclusive) and the specified bound (exclusive). | default boolean | nextBoolean() Returns a pseudorandomly chosen boolean value. | default void | nextBytes(byte[] bytes) Fills a user-supplied byte array with generated byte values pseudorandomly chosen uniformly from the range of values between -128 (inclusive) and 127 (inclusive). | default double | nextDouble() Returns a pseudorandom double value between zero (inclusive) and one (exclusive). | default double | nextDouble(double bound) Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive). | default double | nextDouble(double origin, double bound) Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive). | default double | nextExponential() Returns a nonnegative double value pseudorandomly chosen from an exponential distribution whose mean is 1. | default float | nextFloat(float origin, float bound) Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive). | default float | nextFloat() Returns a pseudorandom float value between zero (inclusive) and one (exclusive). | default float | nextFloat(float bound) Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive). | default double | nextGaussian(double mean, double stddev) Returns a double value pseudorandomly chosen from a Gaussian (normal) distribution with a mean and standard deviation specified by the arguments. | default double | nextGaussian() Returns a double value pseudorandomly chosen from a Gaussian (normal) distribution whose mean is 0 and whose standard deviation is 1. | default int | nextInt(int origin, int bound) Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive). | default int | nextInt() Returns a pseudorandomly chosen int value. | default int | nextInt(int bound) Returns a pseudorandomly chosen int value between zero (inclusive) and the specified bound (exclusive). | default long | nextLong(long origin, long bound) Returns a pseudorandomly chosen long value between the specified origin (inclusive) and the specified bound (exclusive). | default long | nextLong(long bound) Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive). | abstract long | nextLong() Returns a pseudorandomly chosen long value. | static RandomGenerator | of(String name) Returns an instance of RandomGenerator that utilizes the name algorithm. | |
Public methods
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.
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) |
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 nextDouble()
.
Parameters |
streamSize | long : the number of values to generate |
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 nextDouble()
.
Implementation Note:
- This method is implemented to be equivalent to
doubles(Long.MAX_VALUE)
.
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) |
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 nextInt()
.
Parameters |
streamSize | long : the number of values to generate |
Returns |
IntStream | a stream of pseudorandom int values |
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; } }
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) |
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 nextInt()
.
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).
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; } }
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) |
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 nextLong()
.
Parameters |
streamSize | long : the number of values to generate |
Returns |
LongStream | a stream of pseudorandom long values |
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 nextLong()
.
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).
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; }
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) |
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; }
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) |
nextBoolean
public boolean nextBoolean ()
Returns the next pseudorandom, uniformly distributed boolean
value from this random number generator's sequence. The general contract of nextBoolean
is that one boolean
value is pseudorandomly generated and returned. The values true
and false
are produced with (approximately) equal probability.
Returns |
boolean | the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence |
nextDouble
public double nextDouble ()
Returns the next pseudorandom, uniformly distributed double
value between 0.0
and 1.0
from this random number generator's sequence.
The general contract of nextDouble
is that one double
value, chosen (approximately) uniformly from the range 0.0d
(inclusive) to 1.0d
(exclusive), is pseudorandomly generated and returned.
Returns |
double | the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence |
nextDouble
public double nextDouble (double bound)
nextDouble
public double nextDouble (double origin, double bound)
Parameters |
origin | double |
bound | double |
nextFloat
public float nextFloat (float origin, float bound)
Parameters |
origin | float |
bound | float |
nextFloat
public float nextFloat ()
Returns the next pseudorandom, uniformly distributed float
value between 0.0
and 1.0
from this random number generator's sequence.
The general contract of nextFloat
is that one float
value, chosen (approximately) uniformly from the range 0.0f
(inclusive) to 1.0f
(exclusive), is pseudorandomly generated and returned. All 224 possible float
values of the form m x 2-24, where m is a positive integer less than 224, are produced with (approximately) equal probability.
Returns |
float | the next pseudorandom, uniformly distributed float value between 0.0f and 1.0f from this random number generator's sequence |
nextFloat
public float nextFloat (float bound)
nextInt
public int nextInt (int origin, int bound)
Parameters |
origin | int |
bound | int |
nextInt
public int nextInt ()
Returns the next pseudorandom, uniformly distributed int
value from this random number generator's sequence. The general contract of nextInt
is that one int
value is pseudorandomly generated and returned. All 232 possible int
values are produced with (approximately) equal probability.
Returns |
int | the next pseudorandom, uniformly distributed int 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.
Parameters |
bound | int : the upper bound (exclusive). Must be positive. |
Returns |
int | the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence |
nextLong
public long nextLong (long origin, long bound)
Parameters |
origin | long |
bound | long |
nextLong
public long nextLong (long bound)
nextLong
public long nextLong ()
Returns the next pseudorandom, uniformly distributed long
value from this random number generator's sequence. The general contract of nextLong
is that one long
value is pseudorandomly generated and returned.
Returns |
long | the next pseudorandom, uniformly distributed long value from this random number generator's sequence |
setSeed
public void setSeed (long seed)
Throws UnsupportedOperationException
. Setting seeds in this generator is not supported.
Parameters |
seed | long : the seed value |
Protected methods
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.
Parameters |
bits | int : random bits |
Returns |
int | the next pseudorandom value from this random number generator's sequence |