Interface Grouper<R,T>

All Superinterfaces:

AutoCloseable, Closeable

public interface Grouper<R,T>
extends Closeable

Interface which processes groups of rows into other groups of rows.

See Also:

• Table.group

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	Grouper.Factory<R,T>	Is used to generate a new Grouper 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, and then the step method is called.
R	begin(R source)	Is called for the first source row in the group, and then the step method is called.
default void	close()	Is called when this Grouper instance is no longer needed.
default void	finished()	Is called after the last source row in the group has been provided, and then the step method is called.
T	step(T target)	Is called to produce the next target row.

Method Details

begin

R begin(R source)
 throws IOException

Is called for the first source row in the group, and then the step method is called.

Parameters:

source - never null

Returns:

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

Throws:

IOException

accumulate

R accumulate(R source)
      throws IOException

Is called for each source row in the group, other than the first one, and then the step method is called.

Parameters:

source - never null

Returns:

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

Throws:

IOException

finished

default void finished()
               throws IOException

Is called after the last source row in the group has been provided, and then the step method is called.

Throws:

IOException

step

T step(T target)
throws IOException

Is called to produce the next target row. Returning null indicates that no target rows remain, and that reading of source group rows can resume.

Parameters:

target - never null; all columns are initially unset

Returns:

null if no target rows remain

Throws:

IOException

close

default void close()
            throws IOException

Is called when this Grouper instance is no longer needed.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException