UserDefinedAggregator (Apache Derby V10.14 Internals)

java.lang.Object
- org.apache.derby.impl.sql.execute.UserDefinedAggregator

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, Formatable, TypedFormat, ExecAggregator
```
public final class UserDefinedAggregator
extends java.lang.Object
implements ExecAggregator
```
Aggregator for user-defined aggregates. Wraps the application-supplied implementation of org.apache.derby.agg.Aggregator.

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type	Field	Description
`private Aggregator`	`_aggregator`
`private boolean`	`_eliminatedNulls`
`private DataTypeDescriptor`	`_resultType`
`private static int`	`FIRST_VERSION`

Constructor Summary

Constructors
Constructor Description

UserDefinedAggregator()
0-arg constructor for Formatable interface

Constructors
Constructor	Description
`UserDefinedAggregator()`	0-arg constructor for Formatable interface

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`accumulate(DataValueDescriptor addend, java.lang.Object ga)`	Iteratively accumulates the addend into the aggregator.
`boolean`	`didEliminateNulls()`	Return true if the aggregation eliminated at least one null from the input data set.
`DataValueDescriptor`	`getResult()`	Return the result of the aggregation. .
`int`	`getTypeFormatId()`	Get the formatID which corresponds to this class.
`private void`	`logAggregatorInstantiationError(java.lang.String aggregateName, java.lang.Throwable t)`	Record an instantiation error trying to load the aggregator class.
`void`	`merge(ExecAggregator addend)`	Merges one aggregator into a another aggregator.
`ExecAggregator`	`newAggregator()`	Return a new initialized copy of this aggregator, any state set by the setup() method of the original Aggregator must be copied into the new aggregator.
`void`	`readExternal(java.io.ObjectInput in)`
`private void`	`setup(java.lang.Class<?> udaClass, DataTypeDescriptor resultType)`	Initialization logic shared by setup() and newAggregator()
`void`	`setup(ClassFactory classFactory, java.lang.String aggregateName, DataTypeDescriptor resultType)`	Set's up the aggregate for processing.
`void`	`writeExternal(java.io.ObjectOutput out)`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - FIRST_VERSION
```
private static final int FIRST_VERSION
```
    See Also:
    
    Constant Field Values
  - _aggregator
```
private Aggregator _aggregator
```
  - _resultType
```
private DataTypeDescriptor _resultType
```
  - _eliminatedNulls
```
private boolean _eliminatedNulls
```
- Constructor Detail
  - UserDefinedAggregator
```
public UserDefinedAggregator()
```
    0-arg constructor for Formatable interface
- Method Detail
  - setup
```
public void setup(ClassFactory classFactory,
                  java.lang.String aggregateName,
                  DataTypeDescriptor resultType)
```
    Description copied from interface: ExecAggregator
    
    Set's up the aggregate for processing.
    
    Specified by:
    
    setup in interface ExecAggregator
    
    Parameters:
    
    classFactory - Database-specific class factory.
    
    aggregateName - For builtin aggregates, this is a SQL aggregate name like MAX. For user-defined aggregates, this is the name of the user-written class which implements org.apache.derby.agg.Aggregator.
    
    resultType - The type returned by the getResult() method.
  - setup
```
private void setup(java.lang.Class<?> udaClass,
                   DataTypeDescriptor resultType)
```
    Initialization logic shared by setup() and newAggregator()
  - didEliminateNulls
```
public boolean didEliminateNulls()
```
    Description copied from interface: ExecAggregator
    
    Return true if the aggregation eliminated at least one null from the input data set.
    
    Specified by:
    
    didEliminateNulls in interface ExecAggregator
  - accumulate
```
public void accumulate(DataValueDescriptor addend,
                       java.lang.Object ga)
                throws StandardException
```
    Description copied from interface: ExecAggregator
    
    Iteratively accumulates the addend into the aggregator. Called on each member of the set of values that is being aggregated.
    
    Specified by:
    
    accumulate in interface ExecAggregator
    
    Parameters:
    
    addend - the DataValueDescriptor addend (current input to the aggregation)
    
    ga - a result set getter
    
    Throws:
    
    StandardException - on error
  - merge
```
public void merge(ExecAggregator addend)
           throws StandardException
```
    Description copied from interface: ExecAggregator
    Merges one aggregator into a another aggregator. Merges two partial aggregates results into a single result. Needed for:
    - parallel aggregation
    - vector aggregation (GROUP BY)
    - distinct aggregates (e.g. MAX(DISTINCT Col))
    An example of a merge would be: given two COUNT() aggregators, C1 and C2, a merge of C1 into C2 would set C1.count += C2.count. So, given a CountAggregator with a getCount() method that returns its counts, its merge method might look like this:
```
                public void merge(ExecAggregator inputAggregator) throws StandardException
                {
                   count += ((CountAccgregator)inputAggregator).getCount();
                } 
```
    Specified by:
    
    merge in interface ExecAggregator
    
    Parameters:
    
    addend - the other Aggregator (input partial aggregate)
    
    Throws:
    
    StandardException - on error
  - getResult
```
public DataValueDescriptor getResult()
                              throws StandardException
```
    Return the result of the aggregation. .
    
    Specified by:
    
    getResult in interface ExecAggregator
    
    Returns:
    
    the aggregated result (could be a Java null).
    
    Throws:
    
    StandardException - on error
  - newAggregator
```
public ExecAggregator newAggregator()
```
    Description copied from interface: ExecAggregator
    
    Return a new initialized copy of this aggregator, any state set by the setup() method of the original Aggregator must be copied into the new aggregator.
    
    Specified by:
    
    newAggregator in interface ExecAggregator
    
    Returns:
    
    ExecAggregator the new aggregator
  - writeExternal
```
public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException
```
    Specified by:
    
    writeExternal in interface java.io.Externalizable
    
    Throws:
    
    java.io.IOException - on error
  - readExternal
```
public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException
```
    Specified by:
    
    readExternal in interface java.io.Externalizable
    
    Throws:
    
    java.io.IOException - on error
    
    java.lang.ClassNotFoundException
    
    See Also:
    
    Externalizable.readExternal(java.io.ObjectInput)
  - getTypeFormatId
```
public int getTypeFormatId()
```
    Get the formatID which corresponds to this class.
    
    Specified by:
    
    getTypeFormatId in interface TypedFormat
    
    Returns:
    
    the formatID of this class
  - logAggregatorInstantiationError
```
private void logAggregatorInstantiationError(java.lang.String aggregateName,
                                             java.lang.Throwable t)
```
    Record an instantiation error trying to load the aggregator class.

Class UserDefinedAggregator

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

FIRST_VERSION

_aggregator

_resultType

_eliminatedNulls

Constructor Detail

UserDefinedAggregator

Method Detail

setup

setup

didEliminateNulls

accumulate

merge

getResult

newAggregator

writeExternal

readExternal

getTypeFormatId

logAggregatorInstantiationError