Interface - java.util.NavigableMap
Created by : Mr Dk.
2019 / 11 / 13 14:29
Nanjing, Jiangsu, China
Definition
public interface NavigableMap<K,V> extends SortedMap<K,V> {
}
继承自 SortedMap，能够快速返回与给定目标最近的匹配。
lowEntry()- 返回小于给定的 key 的 entryfloorEntry()- 返回小于等于给定 key 的 entryceilingEntry()- 返回大于等于给定 key 的 entryhigherEntry()- 返回大于给定 key 的 entry
如果没有匹配的 key，就返回 null。四个函数还分别有相对应的只返回 key 的版本：这些操作都用于定位，而不是遍历。
descendingMap() 返回一个视角相反的 Map，性能上比正视角的 Map 要慢。
subMap(), headMap(), tailMap() 与 SortedMap 中的函数不同：指定了额外的参数，来表示包含或是不包含边界。此外，还提供了从两端删除最大或最小的 entry 的函数。
/**
* A {@link SortedMap} extended with navigation methods returning the
* closest matches for given search targets. Methods
* {@code lowerEntry}, {@code floorEntry}, {@code ceilingEntry},
* and {@code higherEntry} return {@code Map.Entry} objects
* associated with keys respectively less than, less than or equal,
* greater than or equal, and greater than a given key, returning
* {@code null} if there is no such key. Similarly, methods
* {@code lowerKey}, {@code floorKey}, {@code ceilingKey}, and
* {@code higherKey} return only the associated keys. All of these
* methods are designed for locating, not traversing entries.
*
* <p>A {@code NavigableMap} may be accessed and traversed in either
* ascending or descending key order. The {@code descendingMap}
* method returns a view of the map with the senses of all relational
* and directional methods inverted. The performance of ascending
* operations and views is likely to be faster than that of descending
* ones. Methods {@code subMap}, {@code headMap},
* and {@code tailMap} differ from the like-named {@code
* SortedMap} methods in accepting additional arguments describing
* whether lower and upper bounds are inclusive versus exclusive.
* Submaps of any {@code NavigableMap} must implement the {@code
* NavigableMap} interface.
*
* <p>This interface additionally defines methods {@code firstEntry},
* {@code pollFirstEntry}, {@code lastEntry}, and
* {@code pollLastEntry} that return and/or remove the least and
* greatest mappings, if any exist, else returning {@code null}.
*
* <p>Implementations of entry-returning methods are expected to
* return {@code Map.Entry} pairs representing snapshots of mappings
* at the time they were produced, and thus generally do <em>not</em>
* support the optional {@code Entry.setValue} method. Note however
* that it is possible to change mappings in the associated map using
* method {@code put}.
*
* <p>Methods
* {@link #subMap(Object, Object) subMap(K, K)},
* {@link #headMap(Object) headMap(K)}, and
* {@link #tailMap(Object) tailMap(K)}
* are specified to return {@code SortedMap} to allow existing
* implementations of {@code SortedMap} to be compatibly retrofitted to
* implement {@code NavigableMap}, but extensions and implementations
* of this interface are encouraged to override these methods to return
* {@code NavigableMap}. Similarly,
* {@link #keySet()} can be overriden to return {@code NavigableSet}.
*
* <p>This interface is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @author Doug Lea
* @author Josh Bloch
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
* @since 1.6
*/
/**
* Returns a key-value mapping associated with the greatest key
* strictly less than the given key, or {@code null} if there is
* no such key.
*
* @param key the key
* @return an entry with the greatest key less than {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
Map.Entry<K,V> lowerEntry(K key);
/**
* Returns the greatest key strictly less than the given key, or
* {@code null} if there is no such key.
*
* @param key the key
* @return the greatest key less than {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
K lowerKey(K key);
返回小于指定 key 的最大 entry 或 key。
/**
* Returns a key-value mapping associated with the greatest key
* less than or equal to the given key, or {@code null} if there
* is no such key.
*
* @param key the key
* @return an entry with the greatest key less than or equal to
* {@code key}, or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
Map.Entry<K,V> floorEntry(K key);
/**
* Returns the greatest key less than or equal to the given key,
* or {@code null} if there is no such key.
*
* @param key the key
* @return the greatest key less than or equal to {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
K floorKey(K key);
返回小于等于指定 key 的最大 entry 或 key。
/**
* Returns a key-value mapping associated with the least key
* greater than or equal to the given key, or {@code null} if
* there is no such key.
*
* @param key the key
* @return an entry with the least key greater than or equal to
* {@code key}, or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
Map.Entry<K,V> ceilingEntry(K key);
/**
* Returns the least key greater than or equal to the given key,
* or {@code null} if there is no such key.
*
* @param key the key
* @return the least key greater than or equal to {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
K ceilingKey(K key);
返回大于等于指定 key 的最小 entry 或 key。
/**
* Returns a key-value mapping associated with the least key
* strictly greater than the given key, or {@code null} if there
* is no such key.
*
* @param key the key
* @return an entry with the least key greater than {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
Map.Entry<K,V> higherEntry(K key);
/**
* Returns the least key strictly greater than the given key, or
* {@code null} if there is no such key.
*
* @param key the key
* @return the least key greater than {@code key},
* or {@code null} if there is no such key
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map does not permit null keys
*/
K higherKey(K key);
返回大于指定 key 的最小 entry 或 key。
/**
* Returns a key-value mapping associated with the least
* key in this map, or {@code null} if the map is empty.
*
* @return an entry with the least key,
* or {@code null} if this map is empty
*/
Map.Entry<K,V> firstEntry();
/**
* Returns a key-value mapping associated with the greatest
* key in this map, or {@code null} if the map is empty.
*
* @return an entry with the greatest key,
* or {@code null} if this map is empty
*/
Map.Entry<K,V> lastEntry();
返回 key 最小 / 最大的 entry。
/**
* Removes and returns a key-value mapping associated with
* the least key in this map, or {@code null} if the map is empty.
*
* @return the removed first entry of this map,
* or {@code null} if this map is empty
*/
Map.Entry<K,V> pollFirstEntry();
/**
* Removes and returns a key-value mapping associated with
* the greatest key in this map, or {@code null} if the map is empty.
*
* @return the removed last entry of this map,
* or {@code null} if this map is empty
*/
Map.Entry<K,V> pollLastEntry();
移除 key 最大 / 最小的 entry。
/**
* Returns a reverse order view of the mappings contained in this map.
* The descending map is backed by this map, so changes to the map are
* reflected in the descending map, and vice-versa. If either map is
* modified while an iteration over a collection view of either map
* is in progress (except through the iterator's own {@code remove}
* operation), the results of the iteration are undefined.
*
* <p>The returned map has an ordering equivalent to
* <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
* The expression {@code m.descendingMap().descendingMap()} returns a
* view of {@code m} essentially equivalent to {@code m}.
*
* @return a reverse order view of this map
*/
NavigableMap<K,V> descendingMap();
返回一个视角相反的 NavigableMap
- 但是这个返回的集合与原集合依旧互相作用
- 底层的副本应当是同一份
- 只是
Comparator的逻辑取反了
/**
* Returns a {@link NavigableSet} 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 navigable set view of the keys in this map
*/
NavigableSet<K> navigableKeySet();
返回 Map 中包含的所有 key，迭代器以升序访问。这个集合被 Map 维护，所以对这个集合的操作将会在 Map 中体现，反之亦然。
/**
* Returns a reverse order {@link NavigableSet} view of the keys contained in this map.
* The set's iterator returns the keys in descending 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 reverse order navigable set view of the keys in this map
*/
NavigableSet<K> descendingKeySet();
返回一个视角相反的有序 key Set，性质与正序的 key Set 相同
/**
* Returns a view of the portion of this map whose keys range from
* {@code fromKey} to {@code toKey}. If {@code fromKey} and
* {@code toKey} are equal, the returned map is empty unless
* {@code fromInclusive} and {@code toInclusive} are both true. 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 of its range, or to construct a
* submap either of whose endpoints lie outside its range.
*
* @param fromKey low endpoint of the keys in the returned map
* @param fromInclusive {@code true} if the low endpoint
* is to be included in the returned view
* @param toKey high endpoint of the keys in the returned map
* @param toInclusive {@code true} if the high endpoint
* is to be included in the returned view
* @return a view of the portion of this map whose keys range from
* {@code fromKey} to {@code toKey}
* @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
*/
NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,
K toKey, boolean toInclusive);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code subMap(fromKey, true, toKey, false)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
SortedMap<K,V> subMap(K fromKey, K toKey);
取指定 key 范围内的子集，但可以根据参数确定是否包含边界。
/**
* Returns a view of the portion of this map whose keys are less than (or
* equal to, if {@code inclusive} is true) {@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 of the keys in the returned map
* @param inclusive {@code true} if the high endpoint
* is to be included in the returned view
* @return a view of the portion of this map whose keys are less than
* (or equal to, if {@code inclusive} is true) {@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
*/
NavigableMap<K,V> headMap(K toKey, boolean inclusive);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code headMap(toKey, false)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
SortedMap<K,V> headMap(K toKey);
取比指定的 key 更小的子集，可以根据参数确定是否包含边界。
/**
* Returns a view of the portion of this map whose keys are greater than (or
* equal to, if {@code inclusive} is true) {@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 of the keys in the returned map
* @param inclusive {@code true} if the low endpoint
* is to be included in the returned view
* @return a view of the portion of this map whose keys are greater than
* (or equal to, if {@code inclusive} is true) {@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
*/
NavigableMap<K,V> tailMap(K fromKey, boolean inclusive);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code tailMap(fromKey, true)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
SortedMap<K,V> tailMap(K fromKey);
取比指定 key 更大的子集，可以根据参数确定是否包含边界。