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  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
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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:
  62  * <ol>
  63  *   <li>A void (no arguments) constructor, which creates an empty sorted map
  64  *   sorted according to the natural ordering of its keys.</li>
  65  *   <li>A constructor with a single argument of type {@code Comparator}, which
  66  *   creates an empty sorted map sorted according to the specified comparator.</li>
  67  *   <li>A constructor with a single argument of type {@code Map}, which creates
  68  *   a new map with the same key-value mappings as its argument, sorted
  69  *   according to the keys' natural ordering.</li>
  70  *   <li>A constructor with a single argument of type {@code SortedMap}, which
  71  *   creates a new sorted map with the same key-value mappings and the same
  72  *   ordering as the input sorted map.</li>
  73  * </ol>
  74  * Though nothing enforces this recommendation as interfaces cannot declare
  75  * constructors.
  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 }