Class LongAdder
- All Implemented Interfaces:
- 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.
- Since:
- 1.8
- See Also:
- 
Constructor SummaryConstructors
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Method SummaryModifier and TypeMethodDescriptionvoidadd(long x) Adds the given value.voidEquivalent toadd(-1).doubleReturns thesum()as adoubleafter a widening primitive conversion.floatReturns thesum()as afloatafter a widening primitive conversion.voidEquivalent toadd(1).intintValue()Returns thesum()as anintafter a narrowing primitive conversion.longEquivalent tosum().voidreset()Resets variables maintaining the sum to zero.longsum()Returns the current sum.longtoString()Returns the String representation of thesum().Methods declared in class java.lang.NumberbyteValue, shortValue
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Constructor Details- 
LongAdderpublic LongAdder()Creates a new adder with initial sum of zero.
 
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Method Details- 
addpublic void add(long x) Adds the given value.- Parameters:
- x- the value to add
 
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incrementpublic void increment()Equivalent toadd(1).
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decrementpublic void decrement()Equivalent toadd(-1).
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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.- Returns:
- the sum
 
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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.
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sumThenResetpublic 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
 
- 
toString
- 
longValue
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intValue
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floatValuepublic float floatValue()Returns thesum()as afloatafter a widening primitive conversion.- Specified by:
- floatValuein class- Number
- Returns:
- the numeric value represented by this object after conversion
          to type float.
 
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doubleValuepublic double doubleValue()Returns thesum()as adoubleafter a widening primitive conversion.- Specified by:
- doubleValuein class- Number
- Returns:
- the numeric value represented by this object after conversion
          to type double.
 
 
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