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25  
26  package java.util;
27  
28  /**
29   * A {@link Map} that further provides a <em>total ordering</em> on its keys.
30   * The map is ordered according to the {@linkplain Comparable natural
31   * ordering} of its keys, or by a {@link Comparator} typically
32   * provided at sorted map creation time.  This order is reflected when
33   * iterating over the sorted map's collection views (returned by the
34   * {@code entrySet}, {@code keySet} and {@code values} methods).
35   * Several additional operations are provided to take advantage of the
36   * ordering.  (This interface is the map analogue of {@link SortedSet}.)
37   *
38   * <p>All keys inserted into a sorted map must implement the {@code Comparable}
39   * interface (or be accepted by the specified comparator).  Furthermore, all
40   * such keys must be <em>mutually comparable</em>: {@code k1.compareTo(k2)} (or
41   * {@code comparator.compare(k1, k2)}) must not throw a
42   * {@code ClassCastException} for any keys {@code k1} and {@code k2} in
43   * the sorted map.  Attempts to violate this restriction will cause the
44   * offending method or constructor invocation to throw a
45   * {@code ClassCastException}.
46   *
47   * <p>Note that the ordering maintained by a sorted map (whether or not an
48   * explicit comparator is provided) must be <em>consistent with equals</em> if
49   * the sorted map is to correctly implement the {@code Map} interface.  (See
50   * the {@code Comparable} interface or {@code Comparator} interface for a
51   * precise definition of <em>consistent with equals</em>.)  This is so because
52   * the {@code Map} interface is defined in terms of the {@code equals}
53   * operation, but a sorted map performs all key comparisons using its
54   * {@code compareTo} (or {@code compare}) method, so two keys that are
55   * deemed equal by this method are, from the standpoint of the sorted map,
56   * equal.  The behavior of a tree map <em>is</em> well-defined even if its
57   * ordering is inconsistent with equals; it just fails to obey the general
58   * contract of the {@code Map} interface.
59   *
60   * <p>All general-purpose sorted map implementation classes should provide four
61   * "standard" constructors. It is not possible to enforce this recommendation
62   * though as required constructors cannot be specified by interfaces. The
63   * expected "standard" constructors for all sorted map implementations are:
64   * <ol>
65   *   <li>A void (no arguments) constructor, which creates an empty sorted map
66   *   sorted according to the natural ordering of its keys.</li>
67   *   <li>A constructor with a single argument of type {@code Comparator}, which
68   *   creates an empty sorted map sorted according to the specified comparator.</li>
69   *   <li>A constructor with a single argument of type {@code Map}, which creates
70   *   a new map with the same key-value mappings as its argument, sorted
71   *   according to the keys' natural ordering.</li>
72   *   <li>A constructor with a single argument of type {@code SortedMap}, which
73   *   creates a new sorted map with the same key-value mappings and the same
74   *   ordering as the input sorted map.</li>
75   * </ol>
76   *
77   * <p><strong>Note</strong>: several methods return submaps with restricted key
78   * ranges. Such ranges are <em>half-open</em>, that is, they include their low
79   * endpoint but not their high endpoint (where applicable).  If you need a
80   * <em>closed range</em> (which includes both endpoints), and the key type
81   * allows for calculation of the successor of a given key, merely request
82   * the subrange from {@code lowEndpoint} to
83   * {@code successor(highEndpoint)}.  For example, suppose that {@code m}
84   * is a map whose keys are strings.  The following idiom obtains a view
85   * containing all of the key-value mappings in {@code m} whose keys are
86   * between {@code low} and {@code high}, inclusive:<pre>
87   *   SortedMap&lt;String, V&gt; sub = m.subMap(low, high+"\0");</pre>
88   *
89   * A similar technique can be used to generate an <em>open range</em>
90   * (which contains neither endpoint).  The following idiom obtains a
91   * view containing all of the key-value mappings in {@code m} whose keys
92   * are between {@code low} and {@code high}, exclusive:<pre>
93   *   SortedMap&lt;String, V&gt; sub = m.subMap(low+"\0", high);</pre>
94   *
95   * <p>This interface is a member of the
96   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
97   * Java Collections Framework</a>.
98   *
99   * @param <K> the type of keys maintained by this map
100  * @param <V> the type of mapped values
101  *
102  * @author  Josh Bloch
103  * @see Map
104  * @see TreeMap
105  * @see SortedSet
106  * @see Comparator
107  * @see Comparable
108  * @see Collection
109  * @see ClassCastException
110  * @since 1.2
111  */
112 
113 public interface SortedMap<K,V> extends Map<K,V> {
114     /**
115      * Returns the comparator used to order the keys in this map, or
116      * {@code null} if this map uses the {@linkplain Comparable
117      * natural ordering} of its keys.
118      *
119      * @return the comparator used to order the keys in this map,
120      *         or {@code null} if this map uses the natural ordering
121      *         of its keys
122      */
123     Comparator<? super K> comparator();
124 
125     /**
126      * Returns a view of the portion of this map whose keys range from
127      * {@code fromKey}, inclusive, to {@code toKey}, exclusive.  (If
128      * {@code fromKey} and {@code toKey} are equal, the returned map
129      * is empty.)  The returned map is backed by this map, so changes
130      * in the returned map are reflected in this map, and vice-versa.
131      * The returned map supports all optional map operations that this
132      * map supports.
133      *
134      * <p>The returned map will throw an {@code IllegalArgumentException}
135      * on an attempt to insert a key outside its range.
136      *
137      * @param fromKey low endpoint (inclusive) of the keys in the returned map
138      * @param toKey high endpoint (exclusive) of the keys in the returned map
139      * @return a view of the portion of this map whose keys range from
140      *         {@code fromKey}, inclusive, to {@code toKey}, exclusive
141      * @throws ClassCastException if {@code fromKey} and {@code toKey}
142      *         cannot be compared to one another using this map's comparator
143      *         (or, if the map has no comparator, using natural ordering).
144      *         Implementations may, but are not required to, throw this
145      *         exception if {@code fromKey} or {@code toKey}
146      *         cannot be compared to keys currently in the map.
147      * @throws NullPointerException if {@code fromKey} or {@code toKey}
148      *         is null and this map does not permit null keys
149      * @throws IllegalArgumentException if {@code fromKey} is greater than
150      *         {@code toKey}; or if this map itself has a restricted
151      *         range, and {@code fromKey} or {@code toKey} lies
152      *         outside the bounds of the range
153      */
154     SortedMap<K,V> subMap(K fromKey, K toKey);
155 
156     /**
157      * Returns a view of the portion of this map whose keys are
158      * strictly less than {@code toKey}.  The returned map is backed
159      * by this map, so changes in the returned map are reflected in
160      * this map, and vice-versa.  The returned map supports all
161      * optional map operations that this map supports.
162      *
163      * <p>The returned map will throw an {@code IllegalArgumentException}
164      * on an attempt to insert a key outside its range.
165      *
166      * @param toKey high endpoint (exclusive) of the keys in the returned map
167      * @return a view of the portion of this map whose keys are strictly
168      *         less than {@code toKey}
169      * @throws ClassCastException if {@code toKey} is not compatible
170      *         with this map's comparator (or, if the map has no comparator,
171      *         if {@code toKey} does not implement {@link Comparable}).
172      *         Implementations may, but are not required to, throw this
173      *         exception if {@code toKey} cannot be compared to keys
174      *         currently in the map.
175      * @throws NullPointerException if {@code toKey} is null and
176      *         this map does not permit null keys
177      * @throws IllegalArgumentException if this map itself has a
178      *         restricted range, and {@code toKey} lies outside the
179      *         bounds of the range
180      */
181     SortedMap<K,V> headMap(K toKey);
182 
183     /**
184      * Returns a view of the portion of this map whose keys are
185      * greater than or equal to {@code fromKey}.  The returned map is
186      * backed by this map, so changes in the returned map are
187      * reflected in this map, and vice-versa.  The returned map
188      * supports all optional map operations that this map supports.
189      *
190      * <p>The returned map will throw an {@code IllegalArgumentException}
191      * on an attempt to insert a key outside its range.
192      *
193      * @param fromKey low endpoint (inclusive) of the keys in the returned map
194      * @return a view of the portion of this map whose keys are greater
195      *         than or equal to {@code fromKey}
196      * @throws ClassCastException if {@code fromKey} is not compatible
197      *         with this map's comparator (or, if the map has no comparator,
198      *         if {@code fromKey} does not implement {@link Comparable}).
199      *         Implementations may, but are not required to, throw this
200      *         exception if {@code fromKey} cannot be compared to keys
201      *         currently in the map.
202      * @throws NullPointerException if {@code fromKey} is null and
203      *         this map does not permit null keys
204      * @throws IllegalArgumentException if this map itself has a
205      *         restricted range, and {@code fromKey} lies outside the
206      *         bounds of the range
207      */
208     SortedMap<K,V> tailMap(K fromKey);
209 
210     /**
211      * Returns the first (lowest) key currently in this map.
212      *
213      * @return the first (lowest) key currently in this map
214      * @throws NoSuchElementException if this map is empty
215      */
216     K firstKey();
217 
218     /**
219      * Returns the last (highest) key currently in this map.
220      *
221      * @return the last (highest) key currently in this map
222      * @throws NoSuchElementException if this map is empty
223      */
224     K lastKey();
225 
226     /**
227      * Returns a {@link Set} view of the keys contained in this map.
228      * The set's iterator returns the keys in ascending order.
229      * The set is backed by the map, so changes to the map are
230      * reflected in the set, and vice-versa.  If the map is modified
231      * while an iteration over the set is in progress (except through
232      * the iterator's own {@code remove} operation), the results of
233      * the iteration are undefined.  The set supports element removal,
234      * which removes the corresponding mapping from the map, via the
235      * {@code Iterator.remove}, {@code Set.remove},
236      * {@code removeAll}, {@code retainAll}, and {@code clear}
237      * operations.  It does not support the {@code add} or {@code addAll}
238      * operations.
239      *
240      * @return a set view of the keys contained in this map, sorted in
241      *         ascending order
242      */
243     Set<K> keySet();
244 
245     /**
246      * Returns a {@link Collection} view of the values contained in this map.
247      * The collection's iterator returns the values in ascending order
248      * of the corresponding keys.
249      * The collection is backed by the map, so changes to the map are
250      * reflected in the collection, and vice-versa.  If the map is
251      * modified while an iteration over the collection is in progress
252      * (except through the iterator's own {@code remove} operation),
253      * the results of the iteration are undefined.  The collection
254      * supports element removal, which removes the corresponding
255      * mapping from the map, via the {@code Iterator.remove},
256      * {@code Collection.remove}, {@code removeAll},
257      * {@code retainAll} and {@code clear} operations.  It does not
258      * support the {@code add} or {@code addAll} operations.
259      *
260      * @return a collection view of the values contained in this map,
261      *         sorted in ascending key order
262      */
263     Collection<V> values();
264 
265     /**
266      * Returns a {@link Set} view of the mappings contained in this map.
267      * The set's iterator returns the entries in ascending key order.
268      * The set is backed by the map, so changes to the map are
269      * reflected in the set, and vice-versa.  If the map is modified
270      * while an iteration over the set is in progress (except through
271      * the iterator's own {@code remove} operation, or through the
272      * {@code setValue} operation on a map entry returned by the
273      * iterator) the results of the iteration are undefined.  The set
274      * supports element removal, which removes the corresponding
275      * mapping from the map, via the {@code Iterator.remove},
276      * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
277      * {@code clear} operations.  It does not support the
278      * {@code add} or {@code addAll} operations.
279      *
280      * @return a set view of the mappings contained in this map,
281      *         sorted in ascending key order
282      */
283     Set<Map.Entry<K, V>> entrySet();
284 }