DoubleAdder (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.lang.Number
  • • java.util.concurrent.atomic.DoubleAdder

• All Implemented Interfaces:
  Serializable

public class DoubleAdder
extends Number
implements Serializable
One or more variables that together maintain an initially zerodouble 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.
Since:
1.8
See Also:
Serialized Form

• • Constructor Summary

  Constructors

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

  • Method Summary

  All Methods Instance Methods Concrete Methods

  Modifier and Type	Method	Description
  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().

     * ### Methods inherited from class java.lang.[Number](../../../../java/lang/Number.html "class in java.lang")  
     `[byteValue](../../../../java/lang/Number.html#byteValue--), [shortValue](../../../../java/lang/Number.html#shortValue--)`  
     * ### Methods inherited from class java.lang.[Object](../../../../java/lang/Object.html "class in java.lang")  
     `[clone](../../../../java/lang/Object.html#clone--), [equals](../../../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../../../java/lang/Object.html#finalize--), [getClass](../../../../java/lang/Object.html#getClass--), [hashCode](../../../../java/lang/Object.html#hashCode--), [notify](../../../../java/lang/Object.html#notify--), [notifyAll](../../../../java/lang/Object.html#notifyAll--), [wait](../../../../java/lang/Object.html#wait--), [wait](../../../../java/lang/Object.html#wait-long-), [wait](../../../../java/lang/Object.html#wait-long-int-)`

• • Constructor Detail

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

  • Method Detail

    * #### add  
    public void add(double x)  
    Adds the given value.  
    Parameters:  
    `x` \- the value to add  
    * #### sum  
    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  
    * #### reset  
    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.  
    * #### sumThenReset  
    public double sumThenReset()  
    Equivalent in effect to [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--) followed by [reset()](../../../../java/util/concurrent/atomic/DoubleAdder.html#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  
    * #### toString  
    public [String](../../../../java/lang/String.html "class in java.lang") toString()  
    Returns the String representation of the [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--).  
    Overrides:  
    `[toString](../../../../java/lang/Object.html#toString--)` in class `[Object](../../../../java/lang/Object.html "class in java.lang")`  
    Returns:  
    the String representation of the [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--)  
    * #### doubleValue  
    public double doubleValue()  
    Specified by:  
    `[doubleValue](../../../../java/lang/Number.html#doubleValue--)` in class `[Number](../../../../java/lang/Number.html "class in java.lang")`  
    Returns:  
    the sum  
    * #### longValue  
    public long longValue()  
    Returns the [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--) as a `long` after a narrowing primitive conversion.  
    Specified by:  
    `[longValue](../../../../java/lang/Number.html#longValue--)` in class `[Number](../../../../java/lang/Number.html "class in java.lang")`  
    Returns:  
    the numeric value represented by this object after conversion to type `long`.  
    * #### intValue  
    public int intValue()  
    Returns the [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--) as an `int` after a narrowing primitive conversion.  
    Specified by:  
    `[intValue](../../../../java/lang/Number.html#intValue--)` in class `[Number](../../../../java/lang/Number.html "class in java.lang")`  
    Returns:  
    the numeric value represented by this object after conversion to type `int`.  
    * #### floatValue  
    public float floatValue()  
    Returns the [sum()](../../../../java/util/concurrent/atomic/DoubleAdder.html#sum--) as a `float` after a narrowing primitive conversion.  
    Specified by:  
    `[floatValue](../../../../java/lang/Number.html#floatValue--)` in class `[Number](../../../../java/lang/Number.html "class in java.lang")`  
    Returns:  
    the numeric value represented by this object after conversion to type `float`.

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