content: /**
   * Copyright (C) 2011 The Guava Authors
   *
   * 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 com.fernandocejas.arrow.optional;
  
  import com.fernandocejas.arrow.functions.Function;
  import java.util.Collections;
  import java.util.Set;
  import org.jetbrains.annotations.Nullable;
  
  import static com.fernandocejas.arrow.checks.Preconditions.checkNotNull;
  
  /**
   * Implementation of an {@link Optional} not containing a reference.
   *
   * <p><b>This class contains code derived from <a href="https://github.com/google/guava">Google
   * Guava</a></b>
   */
  final class Absent<T> extends Optional<T> {
    private static final long serialVersionUID = 0;
  
    static final Absent<Object> INSTANCE = new Absent<>();
  
    @SuppressWarnings("unchecked") // implementation is "fully variant"
    static <T> Optional<T> withType() {
      return (Optional<T>) INSTANCE;
    }
  
    private Absent() {
    }
  
    @Override
    public boolean isPresent() {
      return false;
    }
  
    @Override
    public T get() {
      throw new IllegalStateException("Optional.get() cannot be called on an absent value");
    }
  
    @Override
    public T or(T defaultValue) {
      return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
    }
  
    @SuppressWarnings("unchecked") // safe covariant cast
    @Override
    public Optional<T> or(Optional<? extends T> secondChoice) {
      return (Optional<T>) checkNotNull(secondChoice);
    }
  
    @Override
    @Nullable
    public T orNull() {
      return null;
    }
  
    @Override
    public Set<T> asSet() {
      return Collections.emptySet();
    }
  
    @Override
    public <V> Optional<V> transform(Function<? super T, V> function) {
      checkNotNull(function);
      return absent();
    }
  
    @Override
    public boolean equals(@Nullable Object object) {
      return object == this;
    }
  
    @Override
    public int hashCode() {
      return 0x598df91c;
    }
  
    @Override
    public String toString() {
      return "Optional.absent()";
    }
  
    private Object readResolve() {
      return INSTANCE;
    }
  }
  