DoubleAccumulator

java.lang.Object
- java.lang.Number
- - java8.util.concurrent.atomic.DoubleAccumulator

All Implemented Interfaces:

java.io.Serializable
```
public class DoubleAccumulator
extends java.lang.Number
implements java.io.Serializable
```
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.

Since:

1.8

Author:

Doug Lea

See Also:

Serialized Form

Constructor Summary

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

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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.
`java.lang.String`	`toString()` Returns the String representation of the current value.

Methods inherited from class java.lang.Number
byteValue, shortValue

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - DoubleAccumulator
```
public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction,
                         double identity)
```
    Creates a new instance using the given accumulator function and identity element.
    
    Parameters:
    
    accumulatorFunction - a side-effect-free function of two arguments
    
    identity - identity (initial value) for the accumulator function
- Method Detail
  - accumulate
```
public void accumulate(double x)
```
    Updates with the given value.
    
    Parameters:
    
    x - the value
  - get
```
public 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:
    
    the current value
  - reset
```
public 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.
  - getThenReset
```
public 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:
    
    the value before reset
  - toString
```
public java.lang.String toString()
```
    Returns the String representation of the current value.
    
    Overrides:
    
    toString in class java.lang.Object
    
    Returns:
    
    the String representation of the current value
  - doubleValue
```
public double doubleValue()
```
    Equivalent to get().
    
    Specified by:
    
    doubleValue in class java.lang.Number
    
    Returns:
    
    the current value
  - longValue
```
public long longValue()
```
    Returns the current value as a long after a narrowing primitive conversion.
    
    Specified by:
    
    longValue in class java.lang.Number
  - intValue
```
public int intValue()
```
    Returns the current value as an int after a narrowing primitive conversion.
    
    Specified by:
    
    intValue in class java.lang.Number
  - floatValue
```
public float floatValue()
```
    Returns the current value as a float after a narrowing primitive conversion.
    
    Specified by:
    
    floatValue in class java.lang.Number

Class DoubleAccumulator

Constructor Summary

Method Summary

Methods inherited from class java.lang.Number

Methods inherited from class java.lang.Object

Constructor Detail

DoubleAccumulator

Method Detail

accumulate

get

reset

getThenReset

toString

doubleValue

longValue

intValue

floatValue