org.apache.storm.streams.operations

Interface CombinerAggregator<T,A,R>

Type Parameters:

T - the original value type

A - the accumulator type

R - the result type

All Superinterfaces:

Operation, Serializable

All Known Implementing Classes:

Count, LongSum

public interface CombinerAggregator<T,A,R>
extends Operation

Interface for aggregating values.

Method Summary

Modifier and Type	Method and Description
A	apply(A accumulator, T value) Updates the accumulator by applying the current accumulator with the value.
A	init() The initial value of the accumulator to start with.
A	merge(A accum1, A accum2) Merges two accumulators and returns the merged accumulator.
static <T,R> CombinerAggregator<T,R,R>	of(R initialValue, BiFunction<? super R,? super T,? extends R> accumulator, BiFunction<? super R,? super R,? extends R> combiner) A static factory to create a CombinerAggregator based on initial value, accumulator and combiner.
R	result(A accum) Produces a result value out of the accumulator.

Method Detail

of

static <T,R> CombinerAggregator<T,R,R> of(R initialValue,
                                          BiFunction<? super R,? super T,? extends R> accumulator,
                                          BiFunction<? super R,? super R,? extends R> combiner)

A static factory to create a CombinerAggregator based on initial value, accumulator and combiner.

Type Parameters:

T - the value type

R - the result type

Parameters:

initialValue - the initial value of the result to start with

accumulator - a function that accumulates values into a partial result

combiner - a function that combines partially accumulated results

Returns:

the CombinerAggregator

init

A init()

The initial value of the accumulator to start with.

Returns:

the initial value of the accumulator

apply

A apply(A accumulator,
        T value)

Updates the accumulator by applying the current accumulator with the value.

Parameters:

accumulator - the current accumulator

value - the value

Returns:

the updated accumulator

merge

A merge(A accum1,
        A accum2)

Merges two accumulators and returns the merged accumulator.

Parameters:

accum1 - the first accumulator

accum2 - the second accumulator

Returns:

the merged accumulator

result

R result(A accum)

Produces a result value out of the accumulator.

Parameters:

accum - the accumulator

Returns:

the result