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

Public constructors

LongAdder

added in API level 24
public LongAdder ()

Creates a new adder with initial sum of zero.

Public methods

add

added in API level 24
public void add (long x)

Adds the given value.

Parameters
x long: the value to add

decrement

added in API level 24
public void decrement ()

Equivalent to add(-1).

doubleValue

added in API level 24
public 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
public 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
public void increment ()

Equivalent to add(1).

intValue

added in API level 24
public 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
public long longValue ()

Equivalent to sum().

Returns
long the sum

reset

added in API level 24
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.

sum

added in API level 24
public 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
public 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
public String toString ()

Returns the String representation of the sum().

Returns
String the String representation of the sum()