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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 com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.SortedSet;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A sorted set which forwards all its method calls to another sorted set. Subclasses should
 * override one or more methods to modify the behavior of the backing sorted set as desired per the
 * decorator pattern.
 *
 * Warning: The methods of {@code ForwardingSortedSet} forward indiscriminately to
 * the methods of the delegate. For example, overriding {@link #add} alone will not change
 * the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code addAll} as well, either providing your own implementation, or delegating to the
 * provided {@code standardAddAll} method.
 *
 * 
{@code default} method warning: This class does not forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingSortedSet}.
 *
 * 
Each of the {@code standard} methods, where appropriate, uses the set's comparator (or the
 * natural ordering of the elements, if there is no comparator) to test element equality. As a
 * result, if the comparator is not consistent with equals, some of the standard implementations may
 * violate the {@code Set} contract.
 *
 * 
The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Mike Bostock
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingSortedSet extends ForwardingSet implements SortedSet {

  /** Constructor for use by subclasses. */
  protected ForwardingSortedSet() {}

  @Override
  protected abstract SortedSet delegate();

  @Override
  public Comparator comparator() {
    return delegate().comparator();
  }

  @Override
  public E first() {
    return delegate().first();
  }

  @Override
  public SortedSet headSet(E toElement) {
    return delegate().headSet(toElement);
  }

  @Override
  public E last() {
    return delegate().last();
  }

  @Override
  public SortedSet subSet(E fromElement, E toElement) {
    return delegate().subSet(fromElement, toElement);
  }

  @Override
  public SortedSet tailSet(E fromElement) {
    return delegate().tailSet(fromElement);
  }

  // unsafe, but worst case is a CCE is thrown, which callers will be expecting
  @SuppressWarnings("unchecked")
  private int unsafeCompare(@Nullable Object o1, @Nullable Object o2) {
    Comparator comparator = comparator();
    return (comparator == null)
        ? ((Comparable