- java.lang.Object
- 
- java.lang.Number
- 
- java.util.concurrent.atomic.DoubleAccumulator
 
 
- 
- All Implemented Interfaces:
- Serializable
 
 public class DoubleAccumulator extends Number implements Serializable One or more variables that together maintain a runningdoublevalue updated using a supplied function. When updates (methodaccumulate(double)) are contended across threads, the set of variables may grow dynamically to reduce contention. Methodget()(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::maxalong withDouble.NEGATIVE_INFINITYas 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 DoubleAdderprovides analogs of the functionality of this class for the common special case of maintaining sums. The callnew DoubleAdder()is equivalent tonew DoubleAccumulator((x, y) -> x + y, 0.0).This class extends Number, but does not define methods such asequals,hashCodeandcompareTobecause instances are expected to be mutated, and so are not useful as collection keys.- Since:
- 1.8
- See Also:
- Serialized Form
 
- 
- 
Constructor SummaryConstructors Constructor Description DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity)Creates a new instance using the given accumulator function and identity element.
 - 
Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description voidaccumulate(double x)Updates with the given value.doubledoubleValue()Equivalent toget().floatfloatValue()Returns the current value as afloatafter a narrowing primitive conversion.doubleget()Returns the current value.doublegetThenReset()intintValue()Returns the current value as anintafter a narrowing primitive conversion.longlongValue()Returns the current value as alongafter a narrowing primitive conversion.voidreset()Resets variables maintaining updates to the identity value.StringtoString()Returns the String representation of the current value.- 
Methods declared in class java.lang.NumberbyteValue, shortValue
 
- 
 
- 
- 
- 
Constructor Detail- 
DoubleAccumulatorpublic DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity) Creates 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 Detail- 
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
 
 - 
toStringpublic String toString() Returns 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.
 
 
- 
 
-