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/*
 * Copyright (C) 2007 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.collect;

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

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.concurrent.LazyInit;
import java.io.Serializable;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/** An ordering that uses the natural order of the values. */
@GwtCompatible(serializable = true)
@SuppressWarnings({"unchecked", "rawtypes"}) // TODO(kevinb): the right way to explain this??
@ElementTypesAreNonnullByDefault
final class NaturalOrdering extends Ordering> implements Serializable {
  static final NaturalOrdering INSTANCE = new NaturalOrdering();

  // TODO: b/287198172 - Consider eagerly initializing these (but think about serialization).
  @LazyInit @CheckForNull private transient Ordering<@Nullable Comparable> nullsFirst;
  @LazyInit @CheckForNull private transient Ordering<@Nullable Comparable> nullsLast;

  @Override
  public int compare(Comparable left, Comparable right) {
    checkNotNull(left); // for GWT
    checkNotNull(right);
    return ((Comparable