Serializable
public class LongAdder extends Number implements Serializable
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.
Constructor | Description |
---|---|
LongAdder() |
Creates a new adder with initial sum of zero. |
Modifier and Type | Method | Description |
---|---|---|
void |
add |
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() |
|
String |
toString() |
Returns the String representation of the sum() . |
byteValue, shortValue
public LongAdder()
public void add(long x)
x
- the value to addpublic void increment()
add(1)
.public void decrement()
add(-1)
.public long sum()
public void reset()
public long sumThenReset()
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.public String toString()
sum()
.public long longValue()
sum()
.public int intValue()
sum()
as an int
after a narrowing primitive conversion.public float floatValue()
sum()
as a float
after a widening primitive conversion.floatValue
in class Number
float
.public double doubleValue()
sum()
as a double
after a widening primitive conversion.doubleValue
in class Number
double
.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/atomic/LongAdder.html