001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.base.Preconditions.checkArgument;
020
021import com.google.common.annotations.GwtCompatible;
022import java.util.Comparator;
023import java.util.NoSuchElementException;
024import java.util.SortedMap;
025import javax.annotation.CheckForNull;
026import org.checkerframework.checker.nullness.qual.Nullable;
027
028/**
029 * A sorted map which forwards all its method calls to another sorted map. Subclasses should
030 * override one or more methods to modify the behavior of the backing sorted map as desired per the
031 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032 *
033 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMap} forward <i>indiscriminately</i> to
034 * the methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change
035 * the behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should
036 * override {@code putAll} as well, either providing your own implementation, or delegating to the
037 * provided {@code standardPutAll} method.
038 *
039 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
040 * default} methods. Instead, it inherits their default implementations. When those implementations
041 * invoke methods, they invoke methods on the {@code ForwardingSortedMap}.
042 *
043 * <p>Each of the {@code standard} methods, where appropriate, use the comparator of the map to test
044 * equality for both keys and values, unlike {@code ForwardingMap}.
045 *
046 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
047 * thread-safe, even when all of the methods that they depend on are thread-safe.
048 *
049 * @author Mike Bostock
050 * @author Louis Wasserman
051 * @since 2.0
052 */
053@GwtCompatible
054@ElementTypesAreNonnullByDefault
055public abstract class ForwardingSortedMap<K extends @Nullable Object, V extends @Nullable Object>
056    extends ForwardingMap<K, V> implements SortedMap<K, V> {
057  // TODO(lowasser): identify places where thread safety is actually lost
058
059  /** Constructor for use by subclasses. */
060  protected ForwardingSortedMap() {}
061
062  @Override
063  protected abstract SortedMap<K, V> delegate();
064
065  @Override
066  @CheckForNull
067  public Comparator<? super K> comparator() {
068    return delegate().comparator();
069  }
070
071  @Override
072  @ParametricNullness
073  public K firstKey() {
074    return delegate().firstKey();
075  }
076
077  @Override
078  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
079    return delegate().headMap(toKey);
080  }
081
082  @Override
083  @ParametricNullness
084  public K lastKey() {
085    return delegate().lastKey();
086  }
087
088  @Override
089  public SortedMap<K, V> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
090    return delegate().subMap(fromKey, toKey);
091  }
092
093  @Override
094  public SortedMap<K, V> tailMap(@ParametricNullness K fromKey) {
095    return delegate().tailMap(fromKey);
096  }
097
098  /**
099   * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of {@code
100   * ForwardingSortedMap}. In many cases, you may wish to override {@link
101   * ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
102   *
103   * @since 15.0
104   */
105  protected class StandardKeySet extends Maps.SortedKeySet<K, V> {
106    /** Constructor for use by subclasses. */
107    public StandardKeySet() {
108      super(ForwardingSortedMap.this);
109    }
110  }
111
112  // unsafe, but worst case is a CCE or NPE is thrown, which callers will be expecting
113  @SuppressWarnings({"unchecked", "nullness"})
114  static int unsafeCompare(
115      @CheckForNull Comparator<?> comparator, @CheckForNull Object o1, @CheckForNull Object o2) {
116    if (comparator == null) {
117      return ((Comparable<@Nullable Object>) o1).compareTo(o2);
118    } else {
119      return ((Comparator<@Nullable Object>) comparator).compare(o1, o2);
120    }
121  }
122
123  /**
124   * A sensible definition of {@link #containsKey} in terms of the {@code firstKey()} method of
125   * {@link #tailMap}. If you override {@link #tailMap}, you may wish to override {@link
126   * #containsKey} to forward to this implementation.
127   *
128   * @since 7.0
129   */
130  @Override
131  protected boolean standardContainsKey(@CheckForNull Object key) {
132    try {
133      // any CCE or NPE will be caught
134      @SuppressWarnings({"unchecked", "nullness"})
135      SortedMap<@Nullable Object, V> self = (SortedMap<@Nullable Object, V>) this;
136      Object ceilingKey = self.tailMap(key).firstKey();
137      return unsafeCompare(comparator(), ceilingKey, key) == 0;
138    } catch (ClassCastException | NoSuchElementException | NullPointerException e) {
139      return false;
140    }
141  }
142
143  /**
144   * A sensible default implementation of {@link #subMap(Object, Object)} in terms of {@link
145   * #headMap(Object)} and {@link #tailMap(Object)}. In some situations, you may wish to override
146   * {@link #subMap(Object, Object)} to forward to this implementation.
147   *
148   * @since 7.0
149   */
150  protected SortedMap<K, V> standardSubMap(K fromKey, K toKey) {
151    checkArgument(unsafeCompare(comparator(), fromKey, toKey) <= 0, "fromKey must be <= toKey");
152    return tailMap(fromKey).headMap(toKey);
153  }
154}