ProjectionAccumulator (Hibernate Search Engine 6.1.0.Beta1 API)

Type Parameters:

F - The type of (unconverted) field values.

V - The type of field values after the projection converter was applied.

U - The type of the temporary storage for collected field values of type F.

R - The type of the final result containing values of type V.

All Known Implementing Classes:

ListProjectionAccumulator, SingleValuedProjectionAccumulator
```
public interface ProjectionAccumulator<F,V,U,R>
```
A variation on Collector suitable for projections on field values.
Compared to Collector:
- There is no concept of parallel execution.
- All operations are expected to be non-blocking, except for finish(Object, ProjectionConverter, FromDocumentValueConvertContext)

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface ProjectionAccumulator.Provider<V,R>
Provides an accumulator for a given underlying field type (F).

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`U`	`accumulate(U accumulated, F value)`	Folds a new value in the given accumulated container.
`U`	`createInitial()`	Creates the initial accumulated container.
`R`	`finish(U accumulated, ProjectionConverter<? super F,? extends V> converter, FromDocumentValueConvertContext context)`	Finishes the collecting, converting the accumulated container into the final result.

- Method Detail
  - createInitial
```
U createInitial()
```
    Creates the initial accumulated container.
    This operation should be non-blocking.
    
    Returns:
    
    The initial accumulated container, to pass to the first call to accumulate(Object, Object).
  - accumulate
```
U accumulate(U accumulated,
             F value)
```
    Folds a new value in the given accumulated container.
    This operation should be non-blocking.
    
    Parameters:
    
    accumulated - The accumulated value so far. For the first call, this is a value returned by createInitial(). For the next calls, this is the value returned by the previous call to accumulate(Object, Object).
    
    value - The value to accumulate.
    
    Returns:
    
    The new accumulated value.
  - finish
```
R finish(U accumulated,
         ProjectionConverter<? super F,? extends V> converter,
         FromDocumentValueConvertContext context)
```
    Finishes the collecting, converting the accumulated container into the final result.
    This operation may be blocking.
    
    Parameters:
    
    accumulated - The temporary storage created by createInitial() and populated by successive calls to accumulate(Object, Object).
    
    converter - The projection converter (from F to V).
    
    context - The context to be passed to the projection converter.
    
    Returns:
    
    The final result of the collecting.