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Added in API level 24

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

LongAdder

public class LongAdder
extends Number implements Serializable

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

One or more variables that together maintain an initially zero long sum. When updates (method add(long)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method sum() (or, equivalently, longValue()) returns the current total combined across the variables maintaining the sum.

This class is usually preferable to AtomicLong when multiple threads update a common sum 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.

LongAdders can be used with a ConcurrentHashMap to maintain a scalable frequency map (a form of histogram or multiset). For example, to add a count to a ConcurrentHashMap<String,LongAdder> freqs, initializing if not already present, you can use freqs.computeIfAbsent(key, k -> new LongAdder()).increment();

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
`LongAdder()` Creates a new adder with initial sum of zero.

Public methods
`void`	`add(long x)` Adds the given value.
`void`	`decrement()` Equivalent to `add(-1)`.
`double`	`doubleValue()` Returns the `sum()` as a `double` after a widening primitive conversion.
`float`	`floatValue()` Returns the `sum()` as a `float` after a widening primitive conversion.
`void`	`increment()` Equivalent to `add(1)`.
`int`	`intValue()` Returns the `sum()` as an `int` after a narrowing primitive conversion.
`long`	`longValue()` Equivalent to `sum()`.
`void`	`reset()` Resets variables maintaining the sum to zero.
`long`	`sum()` Returns the current sum.
`long`	`sumThenReset()` Equivalent in effect to `sum()` followed by `reset()`.
`String`	`toString()` Returns the String representation of the `sum()`.

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

LongAdder

Added in API level 24

LongAdder ()

Creates a new adder with initial sum of zero.

Public methods

add

Added in API level 24

void add (long x)

Adds the given value.

Parameters
`x`	`long`: the value to add

decrement

Added in API level 24

void decrement ()

Equivalent to add(-1).

doubleValue

Added in API level 24

double doubleValue ()

Returns the sum() as a double after a widening primitive conversion.

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

floatValue

Added in API level 24

float floatValue ()

Returns the sum() as a float after a widening primitive conversion.

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

increment

Added in API level 24

void increment ()

Equivalent to add(1).

intValue

Added in API level 24

int intValue ()

Returns the sum() 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 ()

Equivalent to sum().

Returns
`long`	the sum

reset

Added in API level 24

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.

sum

Added in API level 24

long 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.

Returns
`long`	the sum

sumThenReset

Added in API level 24

long 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
`long`	the sum

toString

Added in API level 24

String toString ()

Returns the String representation of the sum().

Returns
`String`	the String representation of the `sum()`