Class DoubleAdder
java.lang.Object
java.lang.Number
java.util.concurrent.atomic.DoubleAdder
 All Implemented Interfaces:
Serializable
One or more variables that together maintain an initially zero
double
sum. When updates (method add(double)
) are
contended across threads, the set of variables may grow dynamically
to reduce contention. Method sum()
(or, equivalently doubleValue()
) returns the current total combined across the
variables maintaining the sum. 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.
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.
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

Method Summary
Modifier and TypeMethodDescriptionvoid
add
(double x) Adds the given value.double
Equivalent tosum()
.float
Returns thesum()
as afloat
after a narrowing primitive conversion.int
intValue()
Returns thesum()
as anint
after a narrowing primitive conversion.long
Returns thesum()
as along
after a narrowing primitive conversion.void
reset()
Resets variables maintaining the sum to zero.double
sum()
Returns the current sum.double
toString()
Returns the String representation of thesum()
.Methods declared in class java.lang.Number
byteValue, shortValue

Constructor Details

DoubleAdder
public DoubleAdder()Creates a new adder with initial sum of zero.


Method Details

add
public void add(double x) Adds the given value. Parameters:
x
 the value to add

sum
public double sum()Returns the current sum. 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 sum is being calculated might not be incorporated. Also, because floatingpoint arithmetic is not strictly associative, the returned result need not be identical to the value that would be obtained in a sequential series of updates to a single variable. Returns:
 the sum

reset
public void reset()Resets variables maintaining the sum to zero. This method may be a useful alternative to creating a new adder, 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. 
sumThenReset
public double sumThenReset()Equivalent in effect tosum()
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 sum

toString

doubleValue
public double doubleValue()Equivalent tosum()
. Specified by:
doubleValue
in classNumber
 Returns:
 the sum

longValue

intValue

floatValue
public float floatValue()Returns thesum()
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
.
