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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.

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/*
 * 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.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.util.Collections;
import java.util.Set;
import javax.annotation.CheckForNull;

/** Implementation of an {@link Optional} containing a reference. */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class Present extends Optional {
  private final T reference;

  Present(T reference) {
    this.reference = reference;
  }

  @Override
  public boolean isPresent() {
    return true;
  }

  @Override
  public T get() {
    return reference;
  }

  @Override
  public T or(T defaultValue) {
    checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
    return reference;
  }

  @Override
  public Optional or(Optional secondChoice) {
    checkNotNull(secondChoice);
    return this;
  }

  @Override
  public T or(Supplier supplier) {
    checkNotNull(supplier);
    return reference;
  }

  @Override
  public T orNull() {
    return reference;
  }

  @Override
  public Set asSet() {
    return Collections.singleton(reference);
  }

  @Override
  public  Optional transform(Function function) {
    return new Present<>(
        checkNotNull(
            function.apply(reference),
            "the Function passed to Optional.transform() must not return null."));
  }

  @Override
  public boolean equals(@CheckForNull Object object) {
    if (object instanceof Present) {
      Present other = (Present) object;
      return reference.equals(other.reference);
    }
    return false;
  }

  @Override
  public int hashCode() {
    return 0x598df91c + reference.hashCode();
  }

  @Override
  public String toString() {
    return "Optional.of(" + reference + ")";
  }

  private static final long serialVersionUID = 0;
}