/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.beam.sdk.state;
import org.apache.beam.sdk.annotations.Experimental;
import org.apache.beam.sdk.annotations.Experimental.Kind;
import org.apache.beam.sdk.transforms.Combine;
import org.apache.beam.sdk.transforms.GroupByKey;
/**
* A {@link ReadableState} cell that combines multiple input values and outputs a single value of a
* different type.
*
* <p>This generalizes {@link GroupByKey} and {@link Combine} styles of grouping.
*
* @param <InputT> the type of values added to the state
* @param <OutputT> the type of value extracted from the state
*/
@Experimental(Kind.STATE)
public interface GroupingState<InputT, OutputT> extends ReadableState<OutputT>, State {
/** Add a value to the buffer. */
void add(InputT value);
/** Return true if this state is empty. */
ReadableState<Boolean> isEmpty();
@Override
GroupingState<InputT, OutputT> readLater();
}