sdks/java/core/src/main/java/org/apache/beam/sdk/coders/SetCoder.java

/*
 * 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.coders;

import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.beam.sdk.values.TypeDescriptor;
import org.apache.beam.sdk.values.TypeParameter;

/**
 * A {@link SetCoder} encodes any {@link Set} using the format of {@link IterableLikeCoder}. The
 * elements may not be in a deterministic order, depending on the {@code Set} implementation.
 *
 * @param <T> the type of the elements of the set
 */
public class SetCoder<T> extends IterableLikeCoder<T, Set<T>> {

  /** Produces a {@link SetCoder} with the given {@code elementCoder}. */
  public static <T> SetCoder<T> of(Coder<T> elementCoder) {
    return new SetCoder<>(elementCoder);
  }

  /**
   * {@inheritDoc}
   *
   * @throws NonDeterministicException always. Sets are not ordered, but they are encoded in the
   *     order of an arbitrary iteration.
   */
  @Override
  public void verifyDeterministic() throws NonDeterministicException {
    throw new NonDeterministicException(
        this, "Ordering of elements in a set may be non-deterministic.");
  }

  @Override
  public TypeDescriptor<Set<T>> getEncodedTypeDescriptor() {
    return new TypeDescriptor<Set<T>>() {}.where(
        new TypeParameter<T>() {}, getElemCoder().getEncodedTypeDescriptor());
  }

  /////////////////////////////////////////////////////////////////////////////
  // Internal operations below here.

  /**
   * {@inheritDoc}
   *
   * @return A new {@link Set} built from the elements in the {@link List} decoded by {@link
   *     IterableLikeCoder}.
   */
  @Override
  protected final Set<T> decodeToIterable(List<T> decodedElements) {
    return new HashSet<>(decodedElements);
  }

  protected SetCoder(Coder<T> elemCoder) {
    super(elemCoder, "Set");
  }
}