DoubleAdder

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.

Public Constructor Summary

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

Public Method Summary

void
add(double x)
Adds the given value.
double
doubleValue()
Equivalent to sum().
float
floatValue()
Returns the sum() as a float after a narrowing primitive conversion.
int
intValue()
Returns the sum() as an int after a narrowing primitive conversion.
long
longValue()
Returns the sum() as a long after a narrowing primitive conversion.
void
reset()
Resets variables maintaining the sum to zero.
double
sum()
Returns the current sum.
double
sumThenReset()
Equivalent in effect to sum() followed by reset().
String
toString()
Returns the String representation of the sum().

Inherited Method Summary

Public Constructors

public DoubleAdder ()

Creates a new adder with initial sum of zero.

Public Methods

public void add (double x)

Adds the given value.

Parameters
x the value to add

public double doubleValue ()

Equivalent to sum().

Returns
  • the sum

public float floatValue ()

Returns the sum() as a float after a narrowing primitive conversion.

public int intValue ()

Returns the sum() as an int after a narrowing primitive conversion.

public long longValue ()

Returns the sum() as a long after a narrowing primitive conversion.

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.

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 floating-point 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

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

public String toString ()

Returns the String representation of the sum().

Returns
  • the String representation of the sum()