- All Implemented Interfaces:
longsum. When updates (method
add(long)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method
longValue()) returns the current total combined across the variables maintaining the sum.
This class is usually preferable to
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
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
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
compareTo because instances are expected to be mutated, and so are
not useful as collection keys.
- See Also:
- Serialized Form
Constructor SummaryConstructorDescriptionCreates a new adder with initial sum of zero.
Method SummaryModifier and TypeMethodDescription
add(long x)Adds the given value.
reset()Resets variables maintaining the sum to zero.
sum()Returns the current sum.
LongAdderpublic LongAdder()Creates a new adder with initial sum of zero.
addpublic void add(long x)Adds the given value.
x- the value to add
incrementpublic void increment()Equivalent to
decrementpublic void decrement()Equivalent to
sumpublic 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.
- the sum
resetpublic 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.
sumThenResetpublic long sumThenReset()Equivalent in effect to
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.
- the sum
toStringpublic String toString()
longValuepublic long longValue()
intValuepublic int intValue()
floatValuepublic float floatValue()
doubleValuepublic double doubleValue()