Interface Aggregator<R,T>

All Superinterfaces:

AutoCloseable, Closeable

public interface Aggregator<R,T>
extends Closeable

Interface which processes groups of rows into aggregate results.

See Also:

• Table.aggregate

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	Aggregator.Factory<R,T>	Is used to generate a new Aggregator instance for every query against the target table.

Method Summary

Modifier and Type	Method	Description
R	accumulate(R source)	Is called for each source row in the group, other than the first one.
R	begin(R source)	Is called for the first source row in the group.
default void	close()	Is called when this Aggregator instance is no longer needed.
T	finish(T target)	Is called to produce an aggregate result for the current group.

Method Details

begin

R begin(R source)
 throws IOException

Is called for the first source row in the group.

Parameters:

source - never null

Returns:

the next source row instance to use, or null if it was kept by the aggregator

Throws:

IOException

accumulate

R accumulate(R source)
      throws IOException

Is called for each source row in the group, other than the first one.

Parameters:

source - never null

Returns:

the next source row instance to use, or null if it was kept by the aggregator

Throws:

IOException

finish

T finish(T target)
  throws IOException

Is called to produce an aggregate result for the current group. This method is expected to assign the appropriate target column values, except for the primary key. The primary key columns are assigned automatically by the caller.

Parameters:

target - never null; all columns are initially unset

Returns:

null if filtered out

Throws:

IOException

close

default void close()
            throws IOException

Is called when this Aggregator instance is no longer needed.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException