Class LongAdder
- java.lang.Object
-
- java.lang.Number
-
- java.util.concurrent.atomic.LongAdder
- All Implemented Interfaces:
Serializable
public class LongAdder extends Number implements Serializable
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.
- Since:
- 1.8
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
LongAdder() | Creates a new adder with initial sum of zero. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | add(long x) | Adds the given value. |
void | decrement() | Equivalent to |
double | doubleValue() | Returns the |
float | floatValue() | Returns the |
void | increment() | Equivalent to |
int | intValue() | Returns the |
long | longValue() | Equivalent to |
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 |
Methods declared in class java.lang.Number
byteValue, shortValue
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
LongAdder
public LongAdder()
Creates a new adder with initial sum of zero.
Method Detail
add
public void add(long x)
Adds the given value.
- Parameters:
-
x
- the value to add
increment
public void increment()
Equivalent to add(1)
.
decrement
public void decrement()
Equivalent to add(-1)
.
sum
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:
- 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 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:
- the sum
toString
public String toString()
Returns the String representation of the sum()
.
longValue
public long longValue()
Equivalent to sum()
.
intValue
public int intValue()
Returns the sum()
as an int
after a narrowing primitive conversion.
- Specified by:
-
intValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
int
.
floatValue
public float floatValue()
Returns the sum()
as a float
after a widening primitive conversion.
- Specified by:
-
floatValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
float
.
doubleValue
public double doubleValue()
Returns the sum()
as a double
after a widening primitive conversion.
- Specified by:
-
doubleValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
double
.