- java.lang.Object
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- java.util.Random
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- java.util.concurrent.ThreadLocalRandom
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- All Implemented Interfaces:
- Serializable
public class ThreadLocalRandom extends Random
A random number generator isolated to the current thread. Like the globalRandom
generator used by theMath
class, aThreadLocalRandom
is initialized with an internally generated seed that may not otherwise be modified. When applicable, use ofThreadLocalRandom
rather than sharedRandom
objects in concurrent programs will typically encounter much less overhead and contention. Use ofThreadLocalRandom
is particularly appropriate when multiple tasks (for example, each aForkJoinTask
) use random numbers in parallel in thread pools.Usages of this class should typically be of the form:
ThreadLocalRandom.current().nextX(...)
(whereX
isInt
,Long
, etc). When all usages are of this form, it is never possible to accidently share aThreadLocalRandom
across multiple threads.This class also provides additional commonly used bounded random generation methods.
- Since:
- 1.7
- See Also:
- Serialized Form
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-
Method Summary
Methods Modifier and Type Method and Description static ThreadLocalRandom
current()
Returns the current thread'sThreadLocalRandom
.protected int
next(int bits)
Generates the next pseudorandom number.double
nextDouble(double n)
Returns a pseudorandom, uniformly distributeddouble
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)
ThrowsUnsupportedOperationException
.-
Methods inherited from class java.util.Random
nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong
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-
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Method Detail
-
current
public static ThreadLocalRandom current()
Returns the current thread'sThreadLocalRandom
.- Returns:
- the current thread's
ThreadLocalRandom
-
setSeed
public void setSeed(long seed)
ThrowsUnsupportedOperationException
. Setting seeds in this generator is not supported.- Overrides:
setSeed
in classRandom
- 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 anint
value and if the argumentbits
is between1
and32
(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 be0
or1
. The methodnext
is implemented by classRandom
by atomically updating the seed to
and returning(seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)
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.(int)(seed >>> (48 - bits))
.
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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 returnedbound
- 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 returnedbound
- 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 distributeddouble
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 returnedbound
- the upper bound (exclusive)- Returns:
- the next value
- Throws:
IllegalArgumentException
- if least greater than or equal to bound
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