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.Beta;
022import com.google.common.annotations.GwtCompatible;
023import java.util.Comparator;
024import java.util.NoSuchElementException;
025import java.util.SortedMap;
026import org.checkerframework.checker.nullness.compatqual.NullableDecl;
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
054public abstract class ForwardingSortedMap<K, V> extends ForwardingMap<K, V>
055    implements SortedMap<K, V> {
056  // TODO(lowasser): identify places where thread safety is actually lost
057
058  /** Constructor for use by subclasses. */
059  protected ForwardingSortedMap() {}
060
061  @Override
062  protected abstract SortedMap<K, V> delegate();
063
064  @Override
065  public Comparator<? super K> comparator() {
066    return delegate().comparator();
067  }
068
069  @Override
070  public K firstKey() {
071    return delegate().firstKey();
072  }
073
074  @Override
075  public SortedMap<K, V> headMap(K toKey) {
076    return delegate().headMap(toKey);
077  }
078
079  @Override
080  public K lastKey() {
081    return delegate().lastKey();
082  }
083
084  @Override
085  public SortedMap<K, V> subMap(K fromKey, K toKey) {
086    return delegate().subMap(fromKey, toKey);
087  }
088
089  @Override
090  public SortedMap<K, V> tailMap(K fromKey) {
091    return delegate().tailMap(fromKey);
092  }
093
094  /**
095   * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of {@code
096   * ForwardingSortedMap}. In many cases, you may wish to override {@link
097   * ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
098   *
099   * @since 15.0
100   */
101  @Beta
102  protected class StandardKeySet extends Maps.SortedKeySet<K, V> {
103    /** Constructor for use by subclasses. */
104    public StandardKeySet() {
105      super(ForwardingSortedMap.this);
106    }
107  }
108
109  // unsafe, but worst case is a CCE is thrown, which callers will be expecting
110  @SuppressWarnings("unchecked")
111  private int unsafeCompare(Object k1, Object k2) {
112    Comparator<? super K> comparator = comparator();
113    if (comparator == null) {
114      return ((Comparable<Object>) k1).compareTo(k2);
115    } else {
116      return ((Comparator<Object>) comparator).compare(k1, k2);
117    }
118  }
119
120  /**
121   * A sensible definition of {@link #containsKey} in terms of the {@code firstKey()} method of
122   * {@link #tailMap}. If you override {@link #tailMap}, you may wish to override {@link
123   * #containsKey} to forward to this implementation.
124   *
125   * @since 7.0
126   */
127  @Override
128  @Beta
129  protected boolean standardContainsKey(@NullableDecl Object key) {
130    try {
131      // any CCE will be caught
132      @SuppressWarnings("unchecked")
133      SortedMap<Object, V> self = (SortedMap<Object, V>) this;
134      Object ceilingKey = self.tailMap(key).firstKey();
135      return unsafeCompare(ceilingKey, key) == 0;
136    } catch (ClassCastException | NoSuchElementException | NullPointerException e) {
137      return false;
138    }
139  }
140
141  /**
142   * A sensible default implementation of {@link #subMap(Object, Object)} in terms of {@link
143   * #headMap(Object)} and {@link #tailMap(Object)}. In some situations, you may wish to override
144   * {@link #subMap(Object, Object)} to forward to this implementation.
145   *
146   * @since 7.0
147   */
148  @Beta
149  protected SortedMap<K, V> standardSubMap(K fromKey, K toKey) {
150    checkArgument(unsafeCompare(fromKey, toKey) <= 0, "fromKey must be <= toKey");
151    return tailMap(fromKey).headMap(toKey);
152  }
153}