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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.checkArgument;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.Comparator;
import java.util.NoSuchElementException;
import java.util.SortedMap;

import javax.annotation.Nullable;

/**
 * A sorted map which forwards all its method calls to another sorted map.
 * Subclasses should override one or more methods to modify the behavior of
 * the backing sorted map as desired per the decorator pattern.
 *
 * Warning: The methods of {@code ForwardingSortedMap} forward
 * indiscriminately to the methods of the delegate. For example,
 * overriding {@link #put} alone will not change the behavior of {@link
 * #putAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code putAll} as well, either providing your own implementation, or
 * delegating to the provided {@code standardPutAll} method.
 *
 * 
Each of the {@code standard} methods, where appropriate, use the
 * comparator of the map to test equality for both keys and values, unlike
 * {@code ForwardingMap}.
 *
 * 
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 (imported from Google Collections Library)
 */
@GwtCompatible
public abstract class ForwardingSortedMap extends ForwardingMap
    implements SortedMap {
  // TODO(user): identify places where thread safety is actually lost

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

  @Override protected abstract SortedMap delegate();

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

  @Override
  public K firstKey() {
    return delegate().firstKey();
  }

  @Override
  public SortedMap headMap(K toKey) {
    return delegate().headMap(toKey);
  }

  @Override
  public K lastKey() {
    return delegate().lastKey();
  }

  @Override
  public SortedMap subMap(K fromKey, K toKey) {
    return delegate().subMap(fromKey, toKey);
  }

  @Override
  public SortedMap tailMap(K fromKey) {
    return delegate().tailMap(fromKey);
  }

  /**
   * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of
   * {@code ForwardingSortedMap}. In many cases, you may wish to override
   * {@link ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
   *
   * @since 15.0
   */
  @Beta
  protected class StandardKeySet extends Maps.SortedKeySet {
    /** Constructor for use by subclasses. */
    public StandardKeySet() {
      super(ForwardingSortedMap.this);
    }
  }

  // unsafe, but worst case is a CCE is thrown, which callers will be expecting
  @SuppressWarnings("unchecked")
  private int unsafeCompare(Object k1, Object k2) {
    Comparator comparator = comparator();
    if (comparator == null) {
      return ((Comparable