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.kafka.streams.state.internals;
  
  import java.util.NoSuchElementException;
  import java.util.Objects;
  
  /**
   * A container that may be empty, may contain null, or may contain a value.
   * Distinct from {@link java.util.Optional<T>}, since Optional cannot contain null.
   *
   * @param <T>
   */
  public final class Maybe<T> {
      private final T nullableValue;
      private final boolean defined;
  
      public static <T> Maybe<T> defined(final T nullableValue) {
          return new Maybe<>(nullableValue);
      }
  
      public static <T> Maybe<T> undefined() {
          return new Maybe<>();
      }
  
      private Maybe(final T nullableValue) {
          this.nullableValue = nullableValue;
          defined = true;
      }
  
      private Maybe() {
          nullableValue = null;
          defined = false;
      }
  
      public T getNullableValue() {
          if (defined) {
              return nullableValue;
          } else {
              throw new NoSuchElementException();
          }
      }
  
      public boolean isDefined() {
          return defined;
      }
  
      @Override
      public boolean equals(final Object o) {
          if (this == o) return true;
          if (o == null || getClass() != o.getClass()) return false;
          final Maybe<?> maybe = (Maybe<?>) o;
  
          // All undefined maybes are equal
          // All defined null maybes are equal
          return defined == maybe.defined &&
              (!defined || Objects.equals(nullableValue, maybe.nullableValue));
      }
  
      @Override
      public int hashCode() {
          // Since all undefined maybes are equal, we can hard-code their hashCode to -1.
          // Since all defined null maybes are equal, we can hard-code their hashCode to 0.
          return defined ? nullableValue == null ? 0 : nullableValue.hashCode() : -1;
      }
  
      @Override
      public String toString() {
          if (defined) {
              return "DefinedMaybe{" + nullableValue + "}";
          } else {
              return "UndefinedMaybe{}";
          }
      }
  }
  