/*
 * 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.runners.direct;

import java.util.Collection;
import java.util.Collections;
import org.apache.beam.sdk.runners.AppliedPTransform;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionList;

/** A {@link RootInputProvider} that provides a singleton empty bundle. */
class EmptyInputProvider<T> implements RootInputProvider<T, Void, PCollectionList<T>> {
  EmptyInputProvider() {}

  /**
   * {@inheritDoc}.
   *
   * <p>Returns an empty collection.
   */
  @Override
  public Collection<CommittedBundle<Void>> getInitialInputs(
      AppliedPTransform<
              PCollectionList<T>, PCollection<T>, PTransform<PCollectionList<T>, PCollection<T>>>
          transform,
      int targetParallelism) {
    return Collections.emptyList();
  }
}

/*
 * 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.runners.direct;

import java.util.Collection;
import java.util.Collections;
import org.apache.beam.sdk.runners.AppliedPTransform;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionList;

/** A {@link RootInputProvider} that provides no input bundles. */
class EmptyInputProvider<T> implements RootInputProvider<T, Void, PCollectionList<T>> {
  EmptyInputProvider() {}

  /**
   * {@inheritDoc}.
   *
   * <p>Returns an empty collection.
   */
  @Override
  public Collection<CommittedBundle<Void>> getInitialInputs(
      AppliedPTransform<
              PCollectionList<T>, PCollection<T>, PTransform<PCollectionList<T>, PCollection<T>>>
          transform,
      int targetParallelism) {
    return Collections.emptyList();
  }
}

Make EmptyInputProvider Javadoc more precise