- 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 SummaryConstructorsConstructorDescriptionDoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity) Creates a new instance using the given accumulator function and identity element.
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Method SummaryModifier and TypeMethodDescriptionvoidaccumulate(double x) Updates with the given value.doubleEquivalent toget().floatReturns the current value as afloatafter a narrowing primitive conversion.doubleget()Returns the current value.doubleintintValue()Returns the current value as anintafter a narrowing primitive conversion.longReturns the current value as alongafter a narrowing primitive conversion.voidreset()Resets variables maintaining updates to the identity value.toString()Returns the String representation of the current value.Methods declared in class java.lang.NumberbyteValue, shortValue
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Constructor Details- 
DoubleAccumulatorCreates a new instance using the given accumulator function and identity element.- Parameters:
- accumulatorFunction- a side-effect-free function of two arguments
- identity- identity (initial value) for the accumulator function
 
 
- 
- 
Method Details- 
accumulatepublic void accumulate(double x) Updates with the given value.- Parameters:
- x- the value
 
- 
getpublic 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
 
- 
resetpublic 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.
- 
getThenResetpublic 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
 
- 
toStringReturns the String representation of the current value.
- 
doubleValuepublic double doubleValue()Equivalent toget().- Specified by:
- doubleValuein class- Number
- Returns:
- the current value
 
- 
longValuepublic long longValue()Returns the current value as alongafter a narrowing primitive conversion.
- 
intValuepublic int intValue()Returns the current value as anintafter a narrowing primitive conversion.
- 
floatValuepublic float floatValue()Returns the current value as afloatafter a narrowing primitive conversion.- Specified by:
- floatValuein class- Number
- Returns:
- the numeric value represented by this object after conversion
          to type float.
 
 
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