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/*
* Copyright (C) 2015 Google Inc.
*
* Licensed 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 com.google.cloud.dataflow.sdk.values;
import com.google.cloud.dataflow.sdk.Pipeline;
import com.google.cloud.dataflow.sdk.transforms.AppliedPTransform;
import com.google.cloud.dataflow.sdk.transforms.PTransform;
import java.util.Collection;
/**
* The interface for things that might be output from a {@link PTransform}.
*/
public interface POutput {
/**
* Returns the owning {@link Pipeline} of this {@link POutput}.
*/
public Pipeline getPipeline();
/**
* Expands this {@link POutput} into a list of its component output
* {@link PValue PValues}.
*
*
* - A {@link PValue} expands to itself.
* - A tuple or list of {@link PValue PValues} (such as
* {@link PCollectionTuple} or {@link PCollectionList})
* expands to its component {@code PValue PValues}.
*
*
* Not intended to be invoked directly by user code.
*/
public Collection expand();
/**
* Records that this {@code POutput} is an output of the given
* {@code PTransform}.
*
*
For a compound {@code POutput}, it is advised to call
* this method on each component {@code POutput}.
*
*
This is not intended to be invoked by user code, but
* is automatically invoked as part of applying the
* producing {@link PTransform}.
*/
public void recordAsOutput(AppliedPTransform transform);
/**
* As part of applying the producing {@link PTransform}, finalizes this
* output to make it ready for being used as an input and for running.
*
*
This includes ensuring that all {@link PCollection PCollections}
* have {@link Coder Coders} specified or defaulted.
*
*
Automatically invoked whenever this {@link POutput} is used
* as a {@link PInput} to another {@link PTransform}, or if never
* used as a {@link PInput}, when {@link Pipeline#run}
* is called, so users do not normally call this explicitly.
*/
public void finishSpecifyingOutput();
}