1 /*

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     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

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

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    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).

    16  *

    17  * You should have received a copy of the GNU General Public License version

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    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

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    22  * or visit www.oracle.com if you need additional information or have any

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    24  */

    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}/java/util/package-summary.html#CollectionsFramework">

    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 }