程序包 java.util.concurrent.atomic

类 LongAdder

java.lang.Object

java.lang.Number

java.util.concurrent.atomic.LongAdder

所有已实现的接口:

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(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.

从以下版本开始:

1.8

另请参阅:

序列化表格

构造器概要

构造器

构造器	说明
LongAdder()	Creates a new adder with initial sum of zero.

方法概要

限定符和类型	方法	说明
void	add(long x)	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()	Equivalent in effect to sum() followed by reset().
String	toString()	Returns the String representation of the sum().

从类继承的方法 java.lang.Number

byteValue, shortValue

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

构造器详细资料

LongAdder

public LongAdder()

Creates a new adder with initial sum of zero.

方法详细资料

add

public void add(long x)

Adds the given value.

参数:

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.

返回:

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.

返回:

the sum

toString

public String toString()

Returns the String representation of the sum().

覆盖:

toString 在类中 Object

返回:

the String representation of the sum()

longValue

public long longValue()

Equivalent to sum().

指定者:

longValue 在类中 Number

返回:

the sum

intValue

public int intValue()

Returns the sum() as an int after a narrowing primitive conversion.

指定者:

intValue 在类中 Number

返回:

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.

指定者:

floatValue 在类中 Number

返回:

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.

指定者:

doubleValue 在类中 Number

返回:

the numeric value represented by this object after conversion to type double.