MeanStatistic (Apache Hadoop Main 3.3.3 API)

java.lang.Object
- org.apache.hadoop.fs.statistics.MeanStatistic

All Implemented Interfaces:

Serializable, Cloneable
```
@InterfaceAudience.Public
 @InterfaceStability.Evolving
public final class MeanStatistic
extends Object
implements Serializable, Cloneable
```
A mean statistic represented as the sum and the sample count; the mean is calculated on demand.
It can be used to accrue values so as to dynamically update the mean. If so, know that there is no synchronization on the methods.

If a statistic has 0 samples then it is considered to be empty.

All 'empty' statistics are equivalent, independent of the sum value.

For non-empty statistics, sum and sample values must match for equality.

It is serializable and annotated for correct serializations with jackson2.

Thread safety. The operations to add/copy sample data, are thread safe.
So is the mean() method. This ensures that when used to aggregated statistics, the aggregate value and sample count are set and evaluated consistently.

Other methods marked as synchronized because Findbugs overreacts to the idea that some operations to update sum and sample count are synchronized, but that things like equals are not.
See Also:

Serialized Form

Constructor Summary

Constructors
Constructor and Description
`MeanStatistic()` Create an empty statistic.
`MeanStatistic(long samples, long sum)` Constructor, with some resilience against invalid sample counts.
`MeanStatistic(MeanStatistic that)` Create from another statistic.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`MeanStatistic`	`add(MeanStatistic other)` Add another MeanStatistic.
`void`	`addSample(long value)` Add a sample.
`void`	`clear()` Set the values to 0.
`MeanStatistic`	`clone()`
`MeanStatistic`	`copy()` Create a copy of this instance.
`boolean`	`equals(Object o)`
`long`	`getSamples()` Get the sample count.
`long`	`getSum()` Get the sum of samples.
`int`	`hashCode()` The hash code is derived from the mean and sample count: if either is changed the statistic cannot be used as a key for hash tables/maps.
`boolean`	`isEmpty()` Is a statistic empty?
`double`	`mean()` Get the arithmetic mean value.
`void`	`set(MeanStatistic other)` Set the statistic to the values of another.
`void`	`setSamples(long samples)` Set the sample count.
`void`	`setSamplesAndSum(long sampleCount, long newSum)` Set the sum and samples.
`void`	`setSum(long sum)` Set the sum.
`String`	`toString()`

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - MeanStatistic
```
public MeanStatistic(long samples,
                     long sum)
```
    Constructor, with some resilience against invalid sample counts. If the sample count is 0 or less, the sum is set to 0 and the sample count to 0.
    
    Parameters:
    
    samples - sample count.
    
    sum - sum value
  - MeanStatistic
```
public MeanStatistic(MeanStatistic that)
```
    Create from another statistic.
    
    Parameters:
    
    that - source
  - MeanStatistic
```
public MeanStatistic()
```
    Create an empty statistic.
- Method Detail
  - getSum
```
public long getSum()
```
    Get the sum of samples.
    
    Returns:
    
    the sum
  - getSamples
```
public long getSamples()
```
    Get the sample count.
    
    Returns:
    
    the sample count; 0 means empty
  - isEmpty
```
public boolean isEmpty()
```
    Is a statistic empty?
    
    Returns:
    
    true if the sample count is 0
  - clear
```
public void clear()
```
    Set the values to 0.
  - setSamplesAndSum
```
public void setSamplesAndSum(long sampleCount,
                             long newSum)
```
    Set the sum and samples. Synchronized.
    
    Parameters:
    
    sampleCount - new sample count.
    
    newSum - new sum
  - set
```
public void set(MeanStatistic other)
```
    Set the statistic to the values of another. Synchronized.
    
    Parameters:
    
    other - the source.
  - setSum
```
public void setSum(long sum)
```
    Set the sum.
    
    Parameters:
    
    sum - new sum
  - setSamples
```
public void setSamples(long samples)
```
    Set the sample count. If this is less than zero, it is set to zero. This stops an ill-formed JSON entry from breaking deserialization, or get an invalid sample count into an entry.
    
    Parameters:
    
    samples - sample count.
  - mean
```
public double mean()
```
    Get the arithmetic mean value.
    
    Returns:
    
    the mean
  - add
```
public MeanStatistic add(MeanStatistic other)
```
    Add another MeanStatistic.
    
    Parameters:
    
    other - other value
  - addSample
```
public void addSample(long value)
```
    Add a sample. Thread safe.
    
    Parameters:
    
    value - value to add to the sum
  - hashCode
```
public int hashCode()
```
    The hash code is derived from the mean and sample count: if either is changed the statistic cannot be used as a key for hash tables/maps.
    
    Overrides:
    
    hashCode in class Object
    
    Returns:
    
    a hash value
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - clone
```
public MeanStatistic clone()
```
    Overrides:
    
    clone in class Object
  - copy
```
public MeanStatistic copy()
```
    Create a copy of this instance.
    
    Returns:
    
    copy.
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object

Class MeanStatistic

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

MeanStatistic

MeanStatistic

MeanStatistic

Method Detail

getSum

getSamples

isEmpty

clear

setSamplesAndSum

set

setSum

setSamples

mean

add

addSample

hashCode

equals

clone

copy

toString