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;
023
024import java.util.Comparator;
025import java.util.NoSuchElementException;
026import java.util.SortedMap;
027
028import javax.annotation.Nullable;
029
030/**
031 * A sorted map which forwards all its method calls to another sorted map.
032 * Subclasses should override one or more methods to modify the behavior of
033 * the backing sorted map as desired per the <a
034 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
035 *
036 * <p><i>Warning:</i> The methods of {@code ForwardingSortedMap} forward
037 * <i>indiscriminately</i> to the methods of the delegate. For example,
038 * overriding {@link #put} alone <i>will not</i> change the behavior of {@link
039 * #putAll}, which can lead to unexpected behavior. In this case, you should
040 * override {@code putAll} as well, either providing your own implementation, or
041 * delegating to the provided {@code standardPutAll} method.
042 *
043 * <p>Each of the {@code standard} methods, where appropriate, use the
044 * comparator of the map to test equality for both keys and values, unlike
045 * {@code ForwardingMap}.
046 *
047 * <p>The {@code standard} methods and the collection views they return are not
048 * guaranteed to be thread-safe, even when all of the methods that they depend
049 * on are thread-safe.
050 *
051 * @author Mike Bostock
052 * @author Louis Wasserman
053 * @since 2.0
054 */
055@GwtCompatible
056public abstract class ForwardingSortedMap<K, V> extends ForwardingMap<K, V>
057    implements SortedMap<K, V> {
058  // TODO(lowasser): identify places where thread safety is actually lost
059
060  /** Constructor for use by subclasses. */
061  protected ForwardingSortedMap() {}
062
063  @Override
064  protected abstract SortedMap<K, V> delegate();
065
066  @Override
067  public Comparator<? super K> comparator() {
068    return delegate().comparator();
069  }
070
071  @Override
072  public K firstKey() {
073    return delegate().firstKey();
074  }
075
076  @Override
077  public SortedMap<K, V> headMap(K toKey) {
078    return delegate().headMap(toKey);
079  }
080
081  @Override
082  public K lastKey() {
083    return delegate().lastKey();
084  }
085
086  @Override
087  public SortedMap<K, V> subMap(K fromKey, K toKey) {
088    return delegate().subMap(fromKey, toKey);
089  }
090
091  @Override
092  public SortedMap<K, V> tailMap(K fromKey) {
093    return delegate().tailMap(fromKey);
094  }
095
096  /**
097   * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of
098   * {@code ForwardingSortedMap}. In many cases, you may wish to override
099   * {@link ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
100   *
101   * @since 15.0
102   */
103  @Beta
104  protected class StandardKeySet extends Maps.SortedKeySet<K, V> {
105    /** Constructor for use by subclasses. */
106    public StandardKeySet() {
107      super(ForwardingSortedMap.this);
108    }
109  }
110
111  // unsafe, but worst case is a CCE is thrown, which callers will be expecting
112  @SuppressWarnings("unchecked")
113  private int unsafeCompare(Object k1, Object k2) {
114    Comparator<? super K> comparator = comparator();
115    if (comparator == null) {
116      return ((Comparable<Object>) k1).compareTo(k2);
117    } else {
118      return ((Comparator<Object>) comparator).compare(k1, k2);
119    }
120  }
121
122  /**
123   * A sensible definition of {@link #containsKey} in terms of the {@code
124   * firstKey()} method of {@link #tailMap}. If you override {@link #tailMap},
125   * you may wish to override {@link #containsKey} to forward to this
126   * implementation.
127   *
128   * @since 7.0
129   */
130  @Override
131  @Beta
132  protected boolean standardContainsKey(@Nullable Object key) {
133    try {
134      // any CCE will be caught
135      @SuppressWarnings("unchecked")
136      SortedMap<Object, V> self = (SortedMap<Object, V>) this;
137      Object ceilingKey = self.tailMap(key).firstKey();
138      return unsafeCompare(ceilingKey, key) == 0;
139    } catch (ClassCastException e) {
140      return false;
141    } catch (NoSuchElementException e) {
142      return false;
143    } catch (NullPointerException e) {
144      return false;
145    }
146  }
147
148  /**
149   * A sensible default implementation of {@link #subMap(Object, Object)} in
150   * terms of {@link #headMap(Object)} and {@link #tailMap(Object)}. In some
151   * situations, you may wish to override {@link #subMap(Object, Object)} to
152   * forward to this implementation.
153   *
154   * @since 7.0
155   */
156  @Beta
157  protected SortedMap<K, V> standardSubMap(K fromKey, K toKey) {
158    checkArgument(unsafeCompare(fromKey, toKey) <= 0, "fromKey must be <= toKey");
159    return tailMap(fromKey).headMap(toKey);
160  }
161}