Java Reference
In-Depth Information
icLong
instance'sinternallongintegervariableby1andreturnsthepreviousvaluein
one indivisible step.
Additional Concurrency Utilities
As well as supporting the Java 5-introduced concurrency utilities, Java 7 introduces
a pair of concurrency utilities that improve performance, which is achieved in part
by taking full advantage of multiple processors/cores. These utilities consist of the
java.util.concurrent.ThreadLocalRandom
class and the Fork/Join
Framework.
ThreadLocalRandom
The
ThreadLocalRandom
class describes a random number generator that is isol-
ated to the current thread. In other words, it can be accessed from the current thread
only.
Aswiththeglobalrandomnumbergeneratorusedbythe
java.lang.Math
class
(and which I discuss later in this chapter), a
ThreadLocalRandom
instance is ini-
tialized with an internally generated
seed
(starting value) that may not otherwise be
modified. When applicable, use of
ThreadLocalRandom
rather than calls to
Math.random()
inconcurrentprogramswilltypicallyresultinmuchlessoverhead
and contention.
To use this class, first invoke
ThreadLocalRandom
's
static
ThreadLocalRandom current()
method to return the current thread's
ThreadLocalRandom
instance.Continuebyinvokingoneof
ThreadLocalRan-
dom
's“
next
”methods,suchas
double nextDouble(double n)
,whichreturns
a pseudorandom, uniformly distributed
double
value between 0 (inclusive) and the
specifiedvalue
n
(exclusive).Theargumentpassedto
n
istheupperboundontheran-
domnumbertobereturnedandmustbepositive;otherwise,
IllegalArgumentEx-
ception
is thrown.
The following example provides a demonstration via another “
next
” method:
int r = ThreadLocalRandom.current().nextInt(20, 40);
This example invokes
ThreadLocalRandom
's
int nextInt(int least,
int bound)
methodtoreturnapseudorandom,uniformlydistributedvaluebetween
thegiven
least
value(inclusive)and
bound
(exclusive).Inthisexample,
least
is
20
,whichisthesmallestvaluethatcanbereturned,andboundis
40
,whichisonein-
teger greater than the highest value (39) that can be returned.
