Class LongAccumulator
- All Implemented Interfaces:
- Serializable
long
 value updated using a supplied function.  When updates (method
 accumulate(long)) are contended across threads, the set of variables
 may grow dynamically to reduce contention.  Method get()
 (or, equivalently, longValue()) returns the current value
 across the variables maintaining updates.
 This class is usually preferable to AtomicLong when
 multiple threads update a common value that is used for purposes such
 as collecting statistics, not for fine-grained synchronization
 control.  Under low update contention, the two classes have similar
 characteristics. But under high contention, expected throughput of
 this class is significantly higher, at the expense of higher space
 consumption.
 
The order of accumulation within or across threads is not
 guaranteed and cannot be depended upon, so this class is only
 applicable to functions for which the order of accumulation does
 not matter. 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 associative and commutative. 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 
 Long::max along with Long.MIN_VALUE as the identity.
 
Class LongAdder provides analogs of the functionality of
 this class for the common special case of maintaining counts and
 sums.  The call new LongAdder() is equivalent to new
 LongAccumulator((x, y) -> x + y, 0L).
 
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 SummaryConstructorsConstructorDescriptionLongAccumulator(LongBinaryOperator accumulatorFunction, long identity) Creates a new instance using the given accumulator function and identity element.
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Method SummaryModifier and TypeMethodDescriptionvoidaccumulate(long x) Updates with the given value.doubleReturns the current value as adoubleafter a widening primitive conversion.floatReturns the current value as afloatafter a widening primitive conversion.longget()Returns the current value.longintintValue()Returns the current value as anintafter a narrowing primitive conversion.longEquivalent toget().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- 
LongAccumulatorCreates 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
 
 
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Method Details- 
accumulatepublic void accumulate(long x) Updates with the given value.- Parameters:
- x- the value
 
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getpublic long 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
 
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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.
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getThenResetpublic long 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
 
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toString
- 
longValue
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intValuepublic int intValue()Returns the current value as anintafter a narrowing primitive conversion.
- 
floatValuepublic float floatValue()Returns the current value as afloatafter a widening primitive conversion.- Specified by:
- floatValuein class- Number
- Returns:
- the numeric value represented by this object after conversion
          to type float.
 
- 
doubleValuepublic double doubleValue()Returns the current value as adoubleafter a widening primitive conversion.- Specified by:
- doubleValuein class- Number
- Returns:
- the numeric value represented by this object after conversion
          to type double.
 
 
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