NavigableMap

AI-generated Key Takeaways

• The NavigableMap interface extends SortedMap to provide navigation methods for locating entries based on key comparisons.

• It offers ways to access entries in ascending or descending key order, and to obtain submap views.

• Methods such as lowerEntry, floorEntry, ceilingEntry, and higherEntry enable finding closest matches to given keys.

• NavigableMap implementations like TreeMap and ConcurrentSkipListMap provide efficient data structures for sorted data with advanced search capabilities.

• The interface includes methods to retrieve and remove entries based on their key order, using firstEntry, pollFirstEntry, lastEntry, and pollLastEntry.

public interface NavigableMap implements SortedMap<K, V>

Known Indirect Subclasses ConcurrentNavigableMap<K, V>, ConcurrentSkipListMap<K, V>, TreeMap<K, V> ConcurrentNavigableMap<K, V> A ConcurrentMap supporting NavigableMap operations, and recursively so for its navigable sub-maps.  ConcurrentSkipListMap<K, V> A scalable concurrent ConcurrentNavigableMap implementation.  TreeMap<K, V> A Red-Black tree based NavigableMap implementation.

A SortedMap extended with navigation methods returning the closest matches for given search targets. Methods lowerEntry(K), floorEntry(K), ceilingEntry(K), and higherEntry(K) return Map.Entry objects associated with keys respectively less than, less than or equal, greater than or equal, and greater than a given key, returning null if there is no such key. Similarly, methods lowerKey(K), floorKey(K), ceilingKey(K), and higherKey(K) return only the associated keys. All of these methods are designed for locating, not traversing entries.

A NavigableMap may be accessed and traversed in either ascending or descending key order. The 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 subMap(K, boolean, K, boolean), headMap(K, boolean), and tailMap(K, boolean) differ from the like-named SortedMap methods in accepting additional arguments describing whether lower and upper bounds are inclusive versus exclusive. Submaps of any NavigableMap must implement the NavigableMap interface.

This interface additionally defines methods firstEntry(), pollFirstEntry(), lastEntry(), and pollLastEntry() that return and/or remove the least and greatest mappings, if any exist, else returning null.

Implementations of entry-returning methods are expected to return Map.Entry pairs representing snapshots of mappings at the time they were produced, and thus generally do not support the optional Entry.setValue method. Note however that it is possible to change mappings in the associated map using method put.

Methods subMap(K, K), headMap(K), and tailMap(K) are specified to return SortedMap to allow existing implementations of SortedMap to be compatibly retrofitted to implement NavigableMap, but extensions and implementations of this interface are encouraged to override these methods to return NavigableMap. Similarly, SortedMap.keySet() can be overridden to return NavigableSet.

Public Method Summary

abstract Entry<K, V>	ceilingEntry(K key) Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such key.
abstract K	ceilingKey(K key) Returns the least key greater than or equal to the given key, or null if there is no such key.
abstract NavigableSet<K>	descendingKeySet() Returns a reverse order NavigableSet view of the keys contained in this map.
abstract NavigableMap<K, V>	descendingMap() Returns a reverse order view of the mappings contained in this map.
abstract Entry<K, V>	firstEntry() Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
abstract Entry<K, V>	floorEntry(K key) Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.
abstract K	floorKey(K key) Returns the greatest key less than or equal to the given key, or null if there is no such key.
abstract SortedMap<K, V>	headMap(K toKey) Returns a view of the portion of this map whose keys are strictly less than toKey. Equivalent to headMap(toKey, false).
abstract NavigableMap<K, V>	headMap(K toKey, boolean inclusive) Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey.
abstract Entry<K, V>	higherEntry(K key) Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
abstract K	higherKey(K key) Returns the least key strictly greater than the given key, or null if there is no such key.
abstract Entry<K, V>	lastEntry() Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
abstract Entry<K, V>	lowerEntry(K key) Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
abstract K	lowerKey(K key) Returns the greatest key strictly less than the given key, or null if there is no such key.
abstract NavigableSet<K>	navigableKeySet() Returns a NavigableSet view of the keys contained in this map.
abstract Entry<K, V>	pollFirstEntry() Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
abstract Entry<K, V>	pollLastEntry() Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
abstract SortedMap<K, V>	subMap(K fromKey, K toKey) Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive. Equivalent to subMap(fromKey, true, toKey, false).
abstract NavigableMap<K, V>	subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) Returns a view of the portion of this map whose keys range from fromKey to toKey.
abstract NavigableMap<K, V>	tailMap(K fromKey, boolean inclusive) Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey.
abstract SortedMap<K, V>	tailMap(K fromKey) Returns a view of the portion of this map whose keys are greater than or equal to fromKey. Equivalent to tailMap(fromKey, true).

Inherited Method Summary

From interface java.util.SortedMap

abstract Comparator<? super K>	comparator() Returns the comparator used to order the keys in this map, or null if this map uses the {@linkplain Comparable natural ordering} of its keys.
abstract Set<Entry<K, V>>	entrySet() Returns a Set view of the mappings contained in this map.
abstract K	firstKey() Returns the first (lowest) key currently in this map.
abstract SortedMap<K, V>	headMap(K toKey) Returns a view of the portion of this map whose keys are strictly less than toKey.
abstract Set<K>	keySet() Returns a Set view of the keys contained in this map.
abstract K	lastKey() Returns the last (highest) key currently in this map.
abstract SortedMap<K, V>	subMap(K fromKey, K toKey) Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.
abstract SortedMap<K, V>	tailMap(K fromKey) Returns a view of the portion of this map whose keys are greater than or equal to fromKey.
abstract Collection<V>	values() Returns a Collection view of the values contained in this map.

From interface java.util.Map

abstract void	clear() Removes all of the mappings from this map (optional operation).
V	compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).
V	computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null.
V	computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.
abstract boolean	containsKey(Object key) Returns true if this map contains a mapping for the specified key.
abstract boolean	containsValue(Object value) Returns true if this map maps one or more keys to the specified value.
abstract Set<Entry<K, V>>	entrySet() Returns a Set view of the mappings contained in this map.
abstract boolean	equals(Object o) Compares the specified object with this map for equality.
void	forEach(BiConsumer<? super K, ? super V> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
abstract V	get(Object key) Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
V	getOrDefault(Object key, V defaultValue) Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.
abstract int	hashCode() Returns the hash code value for this map.
abstract boolean	isEmpty() Returns true if this map contains no key-value mappings.
abstract Set<K>	keySet() Returns a Set view of the keys contained in this map.
V	merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
abstract V	put(K key, V value) Associates the specified value with the specified key in this map (optional operation).
abstract void	putAll(Map<? extends K, ? extends V> m) Copies all of the mappings from the specified map to this map (optional operation).
V	putIfAbsent(K key, V value) If the specified key is not already associated with a value (or is mapped to null) associates it with the given value and returns null, else returns the current value.
boolean	remove(Object key, Object value) Removes the entry for the specified key only if it is currently mapped to the specified value.
abstract V	remove(Object key) Removes the mapping for a key from this map if it is present (optional operation).
boolean	replace(K key, V oldValue, V newValue) Replaces the entry for the specified key only if currently mapped to the specified value.
V	replace(K key, V value) Replaces the entry for the specified key only if it is currently mapped to some value.
void	replaceAll(BiFunction<? super K, ? super V, ? extends V> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
abstract int	size() Returns the number of key-value mappings in this map.
abstract Collection<V>	values() Returns a Collection view of the values contained in this map.

Public Methods

public abstract Entry<K, V> ceilingEntry (K key)

Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such key.

Parameters

key	the key

Returns

• an entry with the least key greater than or equal to key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract K ceilingKey (K key)

Returns the least key greater than or equal to the given key, or null if there is no such key.

Parameters

key	the key

Returns

• the least key greater than or equal to key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract NavigableSet<K> descendingKeySet ()

Returns a reverse order 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 remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

Returns

• a reverse order navigable set view of the keys in this map

public abstract NavigableMap<K, V> descendingMap ()

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 remove operation), the results of the iteration are undefined.

The returned map has an ordering equivalent to Collections.reverseOrder(comparator()). The expression m.descendingMap().descendingMap() returns a view of m essentially equivalent to m.

Returns

• a reverse order view of this map

public abstract Entry<K, V> firstEntry ()

Returns a key-value mapping associated with the least key in this map, or null if the map is empty.

Returns

• an entry with the least key, or null if this map is empty

public abstract Entry<K, V> floorEntry (K key)

Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.

Parameters

key	the key

Returns

• an entry with the greatest key less than or equal to key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract K floorKey (K key)

Returns the greatest key less than or equal to the given key, or null if there is no such key.

Parameters

key	the key

Returns

• the greatest key less than or equal to key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract SortedMap<K, V> headMap (K toKey)

Returns a view of the portion of this map whose keys are strictly less than 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.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Equivalent to headMap(toKey, false).

Parameters

toKey	high endpoint (exclusive) of the keys in the returned map

Returns

• a view of the portion of this map whose keys are strictly less than toKey

Throws

ClassCastException
NullPointerException
IllegalArgumentException

public abstract NavigableMap<K, V> headMap (K toKey, boolean inclusive)

Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) 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.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Parameters

toKey	high endpoint of the keys in the returned map
inclusive	true if the high endpoint is to be included in the returned view

Returns

• a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey

Throws

ClassCastException	if toKey is not compatible with this map's comparator (or, if the map has no comparator, if toKey does not implement Comparable). Implementations may, but are not required to, throw this exception if toKey cannot be compared to keys currently in the map.
NullPointerException	if toKey is null and this map does not permit null keys
IllegalArgumentException	if this map itself has a restricted range, and toKey lies outside the bounds of the range

public abstract Entry<K, V> higherEntry (K key)

Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.

Parameters

key	the key

Returns

• an entry with the least key greater than key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract K higherKey (K key)

Returns the least key strictly greater than the given key, or null if there is no such key.

Parameters

key	the key

Returns

• the least key greater than key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract Entry<K, V> lastEntry ()

Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.

Returns

• an entry with the greatest key, or null if this map is empty

public abstract Entry<K, V> lowerEntry (K key)

Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.

Parameters

key	the key

Returns

• an entry with the greatest key less than key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract K lowerKey (K key)

Returns the greatest key strictly less than the given key, or null if there is no such key.

Parameters

key	the key

Returns

• the greatest key less than key, or null if there is no such key

Throws

ClassCastException	if the specified key cannot be compared with the keys currently in the map
NullPointerException	if the specified key is null and this map does not permit null keys

public abstract NavigableSet<K> navigableKeySet ()

Returns a 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 remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

Returns

• a navigable set view of the keys in this map

public abstract Entry<K, V> pollFirstEntry ()

Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.

Returns

• the removed first entry of this map, or null if this map is empty

public abstract Entry<K, V> pollLastEntry ()

Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.

Returns

• the removed last entry of this map, or null if this map is empty

public abstract SortedMap<K, V> subMap (K fromKey, K toKey)

Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive. (If fromKey and 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.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Equivalent to subMap(fromKey, true, toKey, false).

Parameters

fromKey	low endpoint (inclusive) of the keys in the returned map
toKey	high endpoint (exclusive) of the keys in the returned map

Returns

• a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive

Throws

ClassCastException
NullPointerException
IllegalArgumentException

public abstract NavigableMap<K, V> subMap (K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

Returns a view of the portion of this map whose keys range from fromKey to toKey. If fromKey and toKey are equal, the returned map is empty unless fromInclusive and 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.

The returned map will throw an 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.

Parameters

fromKey	low endpoint of the keys in the returned map
fromInclusive	true if the low endpoint is to be included in the returned view
toKey	high endpoint of the keys in the returned map
toInclusive	true if the high endpoint is to be included in the returned view

Returns

• a view of the portion of this map whose keys range from fromKey to toKey

Throws

ClassCastException	if fromKey and 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 fromKey or toKey cannot be compared to keys currently in the map.
NullPointerException	if fromKey or toKey is null and this map does not permit null keys
IllegalArgumentException	if fromKey is greater than toKey; or if this map itself has a restricted range, and fromKey or toKey lies outside the bounds of the range

public abstract NavigableMap<K, V> tailMap (K fromKey, boolean inclusive)

Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) 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.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Parameters

fromKey	low endpoint of the keys in the returned map
inclusive	true if the low endpoint is to be included in the returned view

Returns

• a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey

Throws

ClassCastException	if fromKey is not compatible with this map's comparator (or, if the map has no comparator, if fromKey does not implement Comparable). Implementations may, but are not required to, throw this exception if fromKey cannot be compared to keys currently in the map.
NullPointerException	if fromKey is null and this map does not permit null keys
IllegalArgumentException	if this map itself has a restricted range, and fromKey lies outside the bounds of the range

public abstract SortedMap<K, V> tailMap (K fromKey)

Returns a view of the portion of this map whose keys are greater than or equal to 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.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Equivalent to tailMap(fromKey, true).

Parameters

fromKey	low endpoint (inclusive) of the keys in the returned map

Returns

• a view of the portion of this map whose keys are greater than or equal to fromKey

Throws

ClassCastException
NullPointerException
IllegalArgumentException