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Added in API level 24

Summary: Ctors | Methods | Inherited Methods | [Expand All]

DoubleAccumulator

public class DoubleAccumulator
extends Number implements Serializable

java.lang.Object
↳	java.lang.Number
	↳	java.util.concurrent.atomic.DoubleAccumulator

One or more variables that together maintain a running double value updated using a supplied function. When updates (method accumulate(double)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method get() (or, equivalently, doubleValue()) returns the current value across the variables maintaining updates.

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.

The supplied accumulator function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value as its first argument, and the given update as the second argument. For example, to maintain a running maximum value, you could supply Double::max along with Double.NEGATIVE_INFINITY as the identity. 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.

Class DoubleAdder provides analogs of the functionality of this class for the common special case of maintaining sums. The call new DoubleAdder() is equivalent to new DoubleAccumulator((x, y) -> x + y, 0.0).

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.

Summary

Public constructors
`DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity)` Creates a new instance using the given accumulator function and identity element.

Public methods
`void`	`accumulate(double x)` Updates with the given value.
`double`	`doubleValue()` Equivalent to `get()`.
`float`	`floatValue()` Returns the current value as a `float` after a narrowing primitive conversion.
`double`	`get()` Returns the current value.
`double`	`getThenReset()` Equivalent in effect to `get()` followed by `reset()`.
`int`	`intValue()` Returns the current value as an `int` after a narrowing primitive conversion.
`long`	`longValue()` Returns the current value as a `long` after a narrowing primitive conversion.
`void`	`reset()` Resets variables maintaining updates to the identity value.
`String`	`toString()` Returns the String representation of the current value.

Inherited methods

From class


  
    java.lang.Number

From class


  
    java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long millis, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long millis)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

Public constructors

DoubleAccumulator

Added in API level 24

DoubleAccumulator (DoubleBinaryOperator accumulatorFunction, 
                double identity)

Creates a new instance using the given accumulator function and identity element.

Parameters
`accumulatorFunction`	`DoubleBinaryOperator`: a side-effect-free function of two arguments
`identity`	`double`: identity (initial value) for the accumulator function

Public methods

accumulate

Added in API level 24

void accumulate (double x)

Updates with the given value.

Parameters
`x`	`double`: the value

doubleValue

Added in API level 24

double doubleValue ()

Equivalent to get().

Returns
`double`	the current value

floatValue

Added in API level 24

float floatValue ()

Returns the current value as a float after a narrowing primitive conversion.

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

get

Added in API level 24

double 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
`double`	the current value

getThenReset

Added in API level 24

double getThenReset ()

Equivalent in effect to get() 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
`double`	the value before reset

intValue

Added in API level 24

int intValue ()

Returns the current value as an int after a narrowing primitive conversion.

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

longValue

Added in API level 24

long longValue ()

Returns the current value as a long after a narrowing primitive conversion.

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

reset

Added in API level 24

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.

toString

Added in API level 24

String toString ()

Returns the String representation of the current value.

Returns
`String`	the String representation of the current value