Interface - java.util.SortedMap
Created by : Mr Dk.
2019 / 11 / 13 13:37
Nanjing, Jiangsu, China
Definition
public interface SortedMap<K,V> extends Map<K,V> {
}
这种 Map 对 key 有顺序保证：Map 根据 key 的自然顺序或 Comparator 的结果进行排列，这种顺序反映在迭代器迭代 Map 时。
另外有几个额外操作利用了有序这一特性- 插入 Map 的 key 必须是可比较的。key 的比较是通过 compareTo() 而不是 equals() 完成的
/**
* 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}/../technotes/guides/collections/index.html">
* 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
*/
/**
* 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();
返回 Comparator。如果 Comparator 为空，那么按照自然顺序进行排序。
以下是一些根据 key 的排序特性定义的子集操作，子集是集合部分元素的引用。所以对子集的操作会反应在全集中，反之亦然。
/**
* 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);
返回 [fromKey, toKey) 的子集。如果 fromKey == toKey，那么返回的集合为空。
/**
* 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);
返回 key 值 < toKey 的子集。
/**
* 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);
返回 key 值 ≥ fromKey 的子集。
/**
* 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();
返回最小 / 最大的 key。
/**
* 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();
返回 Map 中的所有 key，Set 的迭代器以升序迭代所有的 key。这个集合是被 Map 内部维护的，对该集合的操作会体现在 Map 中，反之亦然。对该集合进行迭代时，如果 Map 被修改 (除了迭代器自身的 remove())，行为未知。
这个集合支持移出，但不支持插入。
/**
* 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();
返回的顺序按照其对应的 key 的升序排列。同样支持移出，但不支持插入，且迭代期间不可并发修改。
/**
* 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();
将 key 和 value 作为一个整体 entry 返回，返回的次序依旧是按照 key 的升序排列。