code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * 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 io.reactivex.rxjava3.flowables;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.Flowable;
  
  /**
   * A {@link Flowable} that has been grouped by key, the value of which can be obtained with {@link #getKey()}.
   * <p>
   * <em>Note:</em> A {@link GroupedFlowable} will cache the items it is to emit until such time as it
   * is subscribed to. For this reason, in order to avoid memory leaks, you should not simply ignore those
   * {@code GroupedFlowable}s that do not concern you. Instead, you can signal to them that they
   * may discard their buffers by applying an operator like {@link Flowable#take take}{@code (0)} to them.
   *
   * @param <K>
   *            the type of the key
   * @param <T>
   *            the type of the items emitted by the {@code GroupedFlowable}
   * @see Flowable#groupBy(io.reactivex.rxjava3.functions.Function)
   * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX documentation: GroupBy</a>
   */
  public abstract class GroupedFlowable<K, T> extends Flowable<T> {
  
      final K key;
  
      /**
       * Constructs a GroupedFlowable with the given key.
       * @param key the key
       */
      protected GroupedFlowable(@Nullable K key) {
          this.key = key;
      }
  
      /**
       * Returns the key that identifies the group of items emitted by this {@code GroupedFlowable}.
       *
       * @return the key that the items emitted by this {@code GroupedFlowable} were grouped by
       */
      @Nullable
      public K getKey() {
          return key;
      }
  }
  