1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.collect;
18
19 import static com.google.common.base.Preconditions.checkArgument;
20
21 import com.google.common.annotations.Beta;
22 import com.google.common.annotations.GwtCompatible;
23 import java.util.Comparator;
24 import java.util.NoSuchElementException;
25 import java.util.SortedMap;
26 import org.checkerframework.checker.nullness.qual.Nullable;
27
28 /**
29 * A sorted map which forwards all its method calls to another sorted map. Subclasses should
30 * override one or more methods to modify the behavior of the backing sorted map as desired per the
31 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
32 *
33 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMap} forward <i>indiscriminately</i> to
34 * the methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change
35 * the behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should
36 * override {@code putAll} as well, either providing your own implementation, or delegating to the
37 * provided {@code standardPutAll} method.
38 *
39 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
40 * default} methods. Instead, it inherits their default implementations. When those implementations
41 * invoke methods, they invoke methods on the {@code ForwardingSortedMap}.
42 *
43 * <p>Each of the {@code standard} methods, where appropriate, use the comparator of the map to test
44 * equality for both keys and values, unlike {@code ForwardingMap}.
45 *
46 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
47 * thread-safe, even when all of the methods that they depend on are thread-safe.
48 *
49 * @author Mike Bostock
50 * @author Louis Wasserman
51 * @since 2.0
52 */
53 @GwtCompatible
54 public abstract class ForwardingSortedMap<K, V> extends ForwardingMap<K, V>
55 implements SortedMap<K, V> {
56 // TODO(lowasser): identify places where thread safety is actually lost
57
58 /** Constructor for use by subclasses. */
59 protected ForwardingSortedMap() {}
60
61 @Override
62 protected abstract SortedMap<K, V> delegate();
63
64 @Override
65 public Comparator<? super K> comparator() {
66 return delegate().comparator();
67 }
68
69 @Override
70 public K firstKey() {
71 return delegate().firstKey();
72 }
73
74 @Override
75 public SortedMap<K, V> headMap(K toKey) {
76 return delegate().headMap(toKey);
77 }
78
79 @Override
80 public K lastKey() {
81 return delegate().lastKey();
82 }
83
84 @Override
85 public SortedMap<K, V> subMap(K fromKey, K toKey) {
86 return delegate().subMap(fromKey, toKey);
87 }
88
89 @Override
90 public SortedMap<K, V> tailMap(K fromKey) {
91 return delegate().tailMap(fromKey);
92 }
93
94 /**
95 * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of {@code
96 * ForwardingSortedMap}. In many cases, you may wish to override {@link
97 * ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
98 *
99 * @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(@Nullable 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 }