- java.lang.Object
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- java.lang.Number
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- java.util.concurrent.atomic.LongAccumulator
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- All Implemented Interfaces:
Serializable
public class LongAccumulator extends Number implements Serializable
One or more variables that together maintain a runninglong
value updated using a supplied function. When updates (methodaccumulate(long)
) are contended across threads, the set of variables may grow dynamically to reduce contention. Methodget()
(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 withLong.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 callnew LongAdder()
is equivalent tonew LongAccumulator((x, y) -> x + y, 0L)
.This class extends
Number
, but does not define methods such asequals
,hashCode
andcompareTo
because instances are expected to be mutated, and so are not useful as collection keys.- Since:
- 1.8
- See Also:
- Serialized Form
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Constructor Summary
Constructors Constructor Description LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)
Creates a new instance using the given accumulator function and identity element.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
accumulate(long x)
Updates with the given value.double
doubleValue()
Returns the current value as adouble
after a widening primitive conversion.float
floatValue()
Returns the current value as afloat
after a widening primitive conversion.long
get()
Returns the current value.long
getThenReset()
int
intValue()
Returns the current value as anint
after a narrowing primitive conversion.long
longValue()
Equivalent toget()
.void
reset()
Resets variables maintaining updates to the identity value.String
toString()
Returns the String representation of the current value.-
Methods declared in class java.lang.Number
byteValue, shortValue
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Constructor Detail
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LongAccumulator
public LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)
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
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Method Detail
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accumulate
public void accumulate(long x)
Updates with the given value.- Parameters:
x
- the value
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get
public 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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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.
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getThenReset
public 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
public String toString()
Returns the String representation of the current value.
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longValue
public long longValue()
Equivalent toget()
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intValue
public int intValue()
Returns the current value as anint
after a narrowing primitive conversion.
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floatValue
public float floatValue()
Returns the current value as afloat
after a widening primitive conversion.- Specified by:
floatValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion
to type
float
.
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doubleValue
public double doubleValue()
Returns the current value as adouble
after a widening primitive conversion.- Specified by:
doubleValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion
to type
double
.
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