Class DoubleAdder
 java.lang.Object

 java.lang.Number

 java.util.concurrent.atomic.DoubleAdder
 All Implemented Interfaces:
Serializable
public class DoubleAdder extends Number implements 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:
 Serialized Form
Constructor Summary
Constructor  Description 

DoubleAdder()  Creates a new adder with initial sum of zero. 
Method Summary
Modifier and Type  Method  Description 

void  add(double x)  Adds the given value. 
double  doubleValue()  Equivalent to 
float  floatValue()  Returns the 
int  intValue()  Returns the 
long  longValue()  Returns the 
void  reset()  Resets variables maintaining the sum to zero. 
double  sum()  Returns the current sum. 
double  sumThenReset()  
String  toString()  Returns the String representation of the 
Methods declared in class java.lang.Number
byteValue, shortValue
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
DoubleAdder
public DoubleAdder()
Creates a new adder with initial sum of zero.
Method Detail
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 to sum()
followed by reset()
. 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
public String toString()
Returns the String representation of the sum()
.
doubleValue
public double doubleValue()
Equivalent to sum()
.
 Specified by:

doubleValue
in classNumber
 Returns:
 the sum
longValue
public long longValue()
Returns the sum()
as a long
after a narrowing primitive conversion.
 Specified by:

longValue
in classNumber
 Returns:
 the numeric value represented by this object after conversion to type
long
.
intValue
public int intValue()
Returns the sum()
as an int
after a narrowing primitive conversion.
 Specified by:

intValue
in classNumber
 Returns:
 the numeric value represented by this object after conversion to type
int
.
floatValue
public float floatValue()
Returns the sum()
as a float
after a narrowing primitive conversion.
 Specified by:

floatValue
in classNumber
 Returns:
 the numeric value represented by this object after conversion to type
float
.