Java tutorial
/* * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; /** * A {@link Map} that further provides a <em>total ordering</em> on its keys. * The map is ordered according to the {@linkplain Comparable natural * ordering} of its keys, or by a {@link Comparator} typically * provided at sorted map creation time. This order is reflected when * iterating over the sorted map's collection views (returned by the * {@code entrySet}, {@code keySet} and {@code values} methods). * Several additional operations are provided to take advantage of the * ordering. (This interface is the map analogue of {@link SortedSet}.) * * <p>All keys inserted into a sorted map must implement the {@code Comparable} * interface (or be accepted by the specified comparator). Furthermore, all * such keys must be <em>mutually comparable</em>: {@code k1.compareTo(k2)} (or * {@code comparator.compare(k1, k2)}) must not throw a * {@code ClassCastException} for any keys {@code k1} and {@code k2} in * the sorted map. Attempts to violate this restriction will cause the * offending method or constructor invocation to throw a * {@code ClassCastException}. * * <p>Note that the ordering maintained by a sorted map (whether or not an * explicit comparator is provided) must be <em>consistent with equals</em> if * the sorted map is to correctly implement the {@code Map} interface. (See * the {@code Comparable} interface or {@code Comparator} interface for a * precise definition of <em>consistent with equals</em>.) This is so because * the {@code Map} interface is defined in terms of the {@code equals} * operation, but a sorted map performs all key comparisons using its * {@code compareTo} (or {@code compare}) method, so two keys that are * deemed equal by this method are, from the standpoint of the sorted map, * equal. The behavior of a tree map <em>is</em> well-defined even if its * ordering is inconsistent with equals; it just fails to obey the general * contract of the {@code Map} interface. * * <p>All general-purpose sorted map implementation classes should provide four * "standard" constructors. It is not possible to enforce this recommendation * though as required constructors cannot be specified by interfaces. The * expected "standard" constructors for all sorted map implementations are: * <ol> * <li>A void (no arguments) constructor, which creates an empty sorted map * sorted according to the natural ordering of its keys.</li> * <li>A constructor with a single argument of type {@code Comparator}, which * creates an empty sorted map sorted according to the specified comparator.</li> * <li>A constructor with a single argument of type {@code Map}, which creates * a new map with the same key-value mappings as its argument, sorted * according to the keys' natural ordering.</li> * <li>A constructor with a single argument of type {@code SortedMap}, which * creates a new sorted map with the same key-value mappings and the same * ordering as the input sorted map.</li> * </ol> * * <p><strong>Note</strong>: several methods return submaps with restricted key * ranges. Such ranges are <em>half-open</em>, that is, they include their low * endpoint but not their high endpoint (where applicable). If you need a * <em>closed range</em> (which includes both endpoints), and the key type * allows for calculation of the successor of a given key, merely request * the subrange from {@code lowEndpoint} to * {@code successor(highEndpoint)}. For example, suppose that {@code m} * is a map whose keys are strings. The following idiom obtains a view * containing all of the key-value mappings in {@code m} whose keys are * between {@code low} and {@code high}, inclusive:<pre> * SortedMap<String, V> sub = m.subMap(low, high+"\0");</pre> * * A similar technique can be used to generate an <em>open range</em> * (which contains neither endpoint). The following idiom obtains a * view containing all of the key-value mappings in {@code m} whose keys * are between {@code low} and {@code high}, exclusive:<pre> * SortedMap<String, V> sub = m.subMap(low+"\0", high);</pre> * * <p>This interface is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @param <K> the type of keys maintained by this map * @param <V> the type of mapped values * * @author Josh Bloch * @see Map * @see TreeMap * @see SortedSet * @see Comparator * @see Comparable * @see Collection * @see ClassCastException * @since 1.2 */ public interface SortedMap<K, V> extends Map<K, V> { /** * Returns the comparator used to order the keys in this map, or * {@code null} if this map uses the {@linkplain Comparable * natural ordering} of its keys. * * @return the comparator used to order the keys in this map, * or {@code null} if this map uses the natural ordering * of its keys */ Comparator<? super K> comparator(); /** * Returns a view of the portion of this map whose keys range from * {@code fromKey}, inclusive, to {@code toKey}, exclusive. (If * {@code fromKey} and {@code toKey} are equal, the returned map * is empty.) The returned map is backed by this map, so changes * in the returned map are reflected in this map, and vice-versa. * The returned map supports all optional map operations that this * map supports. * * <p>The returned map will throw an {@code IllegalArgumentException} * on an attempt to insert a key outside its range. * * @param fromKey low endpoint (inclusive) of the keys in the returned map * @param toKey high endpoint (exclusive) of the keys in the returned map * @return a view of the portion of this map whose keys range from * {@code fromKey}, inclusive, to {@code toKey}, exclusive * @throws ClassCastException if {@code fromKey} and {@code toKey} * cannot be compared to one another using this map's comparator * (or, if the map has no comparator, using natural ordering). * Implementations may, but are not required to, throw this * exception if {@code fromKey} or {@code toKey} * cannot be compared to keys currently in the map. * @throws NullPointerException if {@code fromKey} or {@code toKey} * is null and this map does not permit null keys * @throws IllegalArgumentException if {@code fromKey} is greater than * {@code toKey}; or if this map itself has a restricted * range, and {@code fromKey} or {@code toKey} lies * outside the bounds of the range */ SortedMap<K, V> subMap(K fromKey, K toKey); /** * Returns a view of the portion of this map whose keys are * strictly less than {@code toKey}. The returned map is backed * by this map, so changes in the returned map are reflected in * this map, and vice-versa. The returned map supports all * optional map operations that this map supports. * * <p>The returned map will throw an {@code IllegalArgumentException} * on an attempt to insert a key outside its range. * * @param toKey high endpoint (exclusive) of the keys in the returned map * @return a view of the portion of this map whose keys are strictly * less than {@code toKey} * @throws ClassCastException if {@code toKey} is not compatible * with this map's comparator (or, if the map has no comparator, * if {@code toKey} does not implement {@link Comparable}). * Implementations may, but are not required to, throw this * exception if {@code toKey} cannot be compared to keys * currently in the map. * @throws NullPointerException if {@code toKey} is null and * this map does not permit null keys * @throws IllegalArgumentException if this map itself has a * restricted range, and {@code toKey} lies outside the * bounds of the range */ SortedMap<K, V> headMap(K toKey); /** * Returns a view of the portion of this map whose keys are * greater than or equal to {@code fromKey}. The returned map is * backed by this map, so changes in the returned map are * reflected in this map, and vice-versa. The returned map * supports all optional map operations that this map supports. * * <p>The returned map will throw an {@code IllegalArgumentException} * on an attempt to insert a key outside its range. * * @param fromKey low endpoint (inclusive) of the keys in the returned map * @return a view of the portion of this map whose keys are greater * than or equal to {@code fromKey} * @throws ClassCastException if {@code fromKey} is not compatible * with this map's comparator (or, if the map has no comparator, * if {@code fromKey} does not implement {@link Comparable}). * Implementations may, but are not required to, throw this * exception if {@code fromKey} cannot be compared to keys * currently in the map. * @throws NullPointerException if {@code fromKey} is null and * this map does not permit null keys * @throws IllegalArgumentException if this map itself has a * restricted range, and {@code fromKey} lies outside the * bounds of the range */ SortedMap<K, V> tailMap(K fromKey); /** * Returns the first (lowest) key currently in this map. * * @return the first (lowest) key currently in this map * @throws NoSuchElementException if this map is empty */ K firstKey(); /** * Returns the last (highest) key currently in this map. * * @return the last (highest) key currently in this map * @throws NoSuchElementException if this map is empty */ K lastKey(); /** * Returns a {@link Set} view of the keys contained in this map. * The set's iterator returns the keys in ascending order. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own {@code remove} operation), the results of * the iteration are undefined. The set supports element removal, * which removes the corresponding mapping from the map, via the * {@code Iterator.remove}, {@code Set.remove}, * {@code removeAll}, {@code retainAll}, and {@code clear} * operations. It does not support the {@code add} or {@code addAll} * operations. * * @return a set view of the keys contained in this map, sorted in * ascending order */ Set<K> keySet(); /** * Returns a {@link Collection} view of the values contained in this map. * The collection's iterator returns the values in ascending order * of the corresponding keys. * The collection is backed by the map, so changes to the map are * reflected in the collection, and vice-versa. If the map is * modified while an iteration over the collection is in progress * (except through the iterator's own {@code remove} operation), * the results of the iteration are undefined. The collection * supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Collection.remove}, {@code removeAll}, * {@code retainAll} and {@code clear} operations. It does not * support the {@code add} or {@code addAll} operations. * * @return a collection view of the values contained in this map, * sorted in ascending key order */ Collection<V> values(); /** * Returns a {@link Set} view of the mappings contained in this map. * The set's iterator returns the entries in ascending key order. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own {@code remove} operation, or through the * {@code setValue} operation on a map entry returned by the * iterator) the results of the iteration are undefined. The set * supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Set.remove}, {@code removeAll}, {@code retainAll} and * {@code clear} operations. It does not support the * {@code add} or {@code addAll} operations. * * @return a set view of the mappings contained in this map, * sorted in ascending key order */ Set<Map.Entry<K, V>> entrySet(); }