- java.lang.Object
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- java.lang.Number
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- java.util.concurrent.atomic.LongAdder
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- All Implemented Interfaces:
Serializable
public class LongAdder extends Number implements Serializable
One or more variables that together maintain an initially zerolongsum. When updates (methodadd(long)) are contended across threads, the set of variables may grow dynamically to reduce contention. Methodsum()(or, equivalently,longValue()) returns the current total combined across the variables maintaining the sum.This class is usually preferable to
AtomicLongwhen 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
ConcurrentHashMapto maintain a scalable frequency map (a form of histogram or multiset). For example, to add a count to aConcurrentHashMap<String,LongAdder> freqs, initializing if not already present, you can usefreqs.computeIfAbsent(key, k -> new LongAdder()).increment();This class extends
Number, but does not define methods such asequals,hashCodeandcompareTobecause instances are expected to be mutated, and so are not useful as collection keys.- Since:
- 1.8
- See Also:
- Serialized Form
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Constructor Summary
Constructors Constructor Description LongAdder()Creates a new adder with initial sum of zero.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description voidadd(long x)Adds the given value.voiddecrement()Equivalent toadd(-1).doubledoubleValue()Returns thesum()as adoubleafter a widening primitive conversion.floatfloatValue()Returns thesum()as afloatafter a widening primitive conversion.voidincrement()Equivalent toadd(1).intintValue()Returns thesum()as anintafter a narrowing primitive conversion.longlongValue()Equivalent tosum().voidreset()Resets variables maintaining the sum to zero.longsum()Returns the current sum.longsumThenReset()StringtoString()Returns the String representation of thesum().-
Methods declared in class java.lang.Number
byteValue, shortValue
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Method Detail
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add
public void add(long x)
Adds the given value.- Parameters:
x- the value to add
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increment
public void increment()
Equivalent toadd(1).
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decrement
public void decrement()
Equivalent toadd(-1).
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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
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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.
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sumThenReset
public long sumThenReset()
Equivalent in effect tosum()followed byreset(). 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
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longValue
public long longValue()
Equivalent tosum().
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intValue
public int intValue()
Returns thesum()as anintafter a narrowing primitive conversion.
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floatValue
public float floatValue()
Returns thesum()as afloatafter a widening primitive conversion.- Specified by:
floatValuein classNumber- Returns:
- the numeric value represented by this object after conversion
to type
float.
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doubleValue
public double doubleValue()
Returns thesum()as adoubleafter a widening primitive conversion.- Specified by:
doubleValuein classNumber- Returns:
- the numeric value represented by this object after conversion
to type
double.
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