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

From class java.lang.Number

byte	byteValue() Returns the value of the specified number as a byte, which may involve rounding or truncation.
abstract double	doubleValue() Returns the value of the specified number as a double, which may involve rounding.
abstract float	floatValue() Returns the value of the specified number as a float, which may involve rounding.
abstract int	intValue() Returns the value of the specified number as an int, which may involve rounding or truncation.
abstract long	longValue() Returns the value of the specified number as a long, which may involve rounding or truncation.
short	shortValue() Returns the value of the specified number as a short, which may involve rounding or truncation.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

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.

Returns

• the numeric value represented by this object after conversion to type float.

public int intValue ()

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

Returns

• the numeric value represented by this object after conversion to type int.

public long longValue ()

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

Returns

• the numeric value represented by this object after conversion to type long.

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()