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.internal.operators.observable;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Supplier;
  import io.reactivex.rxjava3.internal.disposables.EmptyDisposable;
  
  import java.util.Objects;
  
  public final class ObservableDefer<T> extends Observable<T> {
      final Supplier<? extends ObservableSource<? extends T>> supplier;
      public ObservableDefer(Supplier<? extends ObservableSource<? extends T>> supplier) {
          this.supplier = supplier;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> observer) {
          ObservableSource<? extends T> pub;
          try {
              pub = Objects.requireNonNull(supplier.get(), "The supplier returned a null ObservableSource");
          } catch (Throwable t) {
              Exceptions.throwIfFatal(t);
              EmptyDisposable.error(t, observer);
              return;
          }
  
          pub.subscribe(observer);
      }
  }
  