- All Implemented Interfaces:
Serializable
double
value updated using a supplied function. When updates (method
accumulate(double)
) are contended across threads, the set of variables
may grow dynamically to reduce contention. Method get()
(or, equivalently, doubleValue()
) returns the current value
across the variables maintaining updates.
This class is usually preferable to alternatives when multiple threads update a common value that is used for purposes such as summary statistics that are frequently updated but less frequently read.
The supplied accumulator function should be side-effect-free,
since it may be re-applied when attempted updates fail due to
contention among threads. For predictable results, the accumulator
function should be commutative and associative within the floating
point tolerance required in usage contexts. The function is applied
with an existing value (or identity) as one argument, and a given
update as the other argument. For example, to maintain a running
maximum value, you could supply Double::max
along with
Double.NEGATIVE_INFINITY
as the identity. The order of
accumulation within or across threads is not guaranteed. Thus, this
class may not be applicable if numerical stability is required,
especially when combining values of substantially different orders
of magnitude.
Class DoubleAdder
provides analogs of the functionality
of this class for the common special case of maintaining sums. The
call new DoubleAdder()
is equivalent to new
DoubleAccumulator((x, y) -> x + y, 0.0)
.
This class extends Number
, but does not define
methods such as equals
, hashCode
and
compareTo
because instances are expected to be mutated, and so are
not useful as collection keys.
- Since:
- 1.8
- See Also:
-
Constructor Summary
ConstructorDescriptionDoubleAccumulator
(DoubleBinaryOperator accumulatorFunction, double identity) Creates a new instance using the given accumulator function and identity element. -
Method Summary
Modifier and TypeMethodDescriptionvoid
accumulate
(double x) Updates with the given value.double
Equivalent toget()
.float
Returns the current value as afloat
after a narrowing primitive conversion.double
get()
Returns the current value.double
int
intValue()
Returns the current value as anint
after a narrowing primitive conversion.long
Returns the current value as along
after a narrowing primitive conversion.void
reset()
Resets variables maintaining updates to the identity value.toString()
Returns the String representation of the current value.Methods declared in class java.lang.Number
byteValue, shortValue
-
Constructor Details
-
DoubleAccumulator
Creates a new instance using the given accumulator function and identity element.- Parameters:
accumulatorFunction
- a side-effect-free function of two argumentsidentity
- identity (initial value) for the accumulator function
-
-
Method Details
-
accumulate
public void accumulate(double x) Updates with the given value.- Parameters:
x
- the value
-
get
public double get()Returns the current value. The returned value is NOT an atomic snapshot; invocation in the absence of concurrent updates returns an accurate result, but concurrent updates that occur while the value is being calculated might not be incorporated.- Returns:
- the current value
-
reset
public void reset()Resets variables maintaining updates to the identity value. This method may be a useful alternative to creating a new updater, but is only effective if there are no concurrent updates. Because this method is intrinsically racy, it should only be used when it is known that no threads are concurrently updating. -
getThenReset
public double getThenReset()Equivalent in effect toget()
followed byreset()
. This method may apply for example during quiescent points between multithreaded computations. If there are updates concurrent with this method, the returned value is not guaranteed to be the final value occurring before the reset.- Returns:
- the value before reset
-
toString
-
doubleValue
public double doubleValue()Equivalent toget()
.- Specified by:
doubleValue
in classNumber
- Returns:
- the current value
-
longValue
public long longValue()Returns the current value as along
after a narrowing primitive conversion. -
intValue
public int intValue()Returns the current value as anint
after a narrowing primitive conversion. -
floatValue
public float floatValue()Returns the current value as afloat
after a narrowing primitive conversion.- Specified by:
floatValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion
to type
float
.
-