content: /*
   * 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.calcite.materialize;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.io.Serializable;
  import java.util.UUID;
  
  /**
   * Unique identifier for a materialization.
   *
   * <p>It is immutable and can only be created by the
   * {@link MaterializationService}. For communicating with the service.
   */
  public class MaterializationKey implements Serializable {
    private final UUID uuid = UUID.randomUUID();
  
    @Override public int hashCode() {
      return uuid.hashCode();
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof MaterializationKey
          && uuid.equals(((MaterializationKey) obj).uuid);
    }
  
    @Override public String toString() {
      return uuid.toString();
    }
  }
  