LongAccumulator

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

All Implemented Interfaces:

java.io.Serializable
```
public class LongAccumulator
extends java.lang.Number
implements java.io.Serializable
```
One or more variables that together maintain a running long value updated using a supplied function. When updates (method accumulate(long)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method get() (or, equivalently, longValue()) returns the current value across the variables maintaining updates.
This class is usually preferable to AtomicLong when multiple threads update a common value that is used for purposes such as collecting statistics, not for fine-grained synchronization control. Under low update contention, the two classes have similar characteristics. But under high contention, expected throughput of this class is significantly higher, at the expense of higher space consumption.
The order of accumulation within or across threads is not guaranteed and cannot be depended upon, so this class is only applicable to functions for which the order of accumulation does not matter. 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 Long::max along with Long.MIN_VALUE as the identity.
Class LongAdder provides analogs of the functionality of this class for the common special case of maintaining counts and sums. The call new LongAdder() is equivalent to new LongAccumulator((x, y) -> x + y, 0L.
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
`LongAccumulator(LongBinaryOperator accumulatorFunction, long 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(long x)` Updates with the given value.
`double`	`doubleValue()` Returns the current value as a `double` after a widening primitive conversion.
`float`	`floatValue()` Returns the current value as a `float` after a widening primitive conversion.
`long`	`get()` Returns the current value.
`long`	`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()` Equivalent to `get()`.
`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
  - LongAccumulator
```
public LongAccumulator(LongBinaryOperator accumulatorFunction,
                       long 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(long x)
```
    Updates with the given value.
    
    Parameters:
    
    x - the value
  - get
```
public long 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 long 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
  - longValue
```
public long longValue()
```
    Equivalent to get().
    
    Specified by:
    
    longValue in class java.lang.Number
    
    Returns:
    
    the current value
  - 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 widening primitive conversion.
    
    Specified by:
    
    floatValue in class java.lang.Number
  - doubleValue
```
public double doubleValue()
```
    Returns the current value as a double after a widening primitive conversion.
    
    Specified by:
    
    doubleValue in class java.lang.Number

Class LongAccumulator

Constructor Summary

Method Summary

Methods inherited from class java.lang.Number

Methods inherited from class java.lang.Object

Constructor Detail

LongAccumulator

Method Detail

accumulate

get

reset

getThenReset

toString

longValue

intValue

floatValue

doubleValue