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    9    * by Oracle in the LICENSE file that accompanied this code.
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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
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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   }

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