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## java.util
Interface NavigableMap<K,V>

Type Parameters:
  `K` - the type of keys maintained by this map
  `V` - the type of mapped values

All Superinterfaces:
  Map<K,V>, SortedMap<K,V>

All Known Subinterfaces:
  ConcurrentNavigableMap<K,V>

All Known Implementing Classes:
  ConcurrentSkipListMap, TreeMap

    public interface NavigableMap<K,V>

extends SortedMap<K,V>

A `SortedMap` extended with navigation methods returning the closest matches for given search targets. Methods `lowerEntry`, `floorEntry`, `ceilingEntry`, and `higherEntry` 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`, `floorKey`, `ceilingKey`, and `higherKey` 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`, `headMap`, and `tailMap` 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 overriden to return `NavigableSet`.

This interface is a member of the Java Collections Framework.

Since:
  1.6

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map
`Map.Entry<K,V>`

Method Summary
`Map.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.
`K` | `ceilingKey(K key)` Returns the least key greater than or equal to the given key, or `null` if there is no such key.
`NavigableSet<K>` | `descendingKeySet()` Returns a reverse order `NavigableSet` view of the keys contained in this map.
`NavigableMap<K,V>` | `descendingMap()` Returns a reverse order view of the mappings contained in this map.
`Map.Entry<K,V>` | `firstEntry()` Returns a key-value mapping associated with the least key in this map, or `null` if the map is empty.
`Map.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.
`K` | `floorKey(K key)` Returns the greatest key less than or equal to the given key, or `null` if there is no such key.
`SortedMap<K,V>` | `headMap(K toKey)` Returns a view of the portion of this map whose keys are strictly less than `toKey`.
`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`.
`Map.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.
`K` | `higherKey(K key)` Returns the least key strictly greater than the given key, or `null` if there is no such key.
`Map.Entry<K,V>` | `lastEntry()` Returns a key-value mapping associated with the greatest key in this map, or `null` if the map is empty.
`Map.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.
`K` | `lowerKey(K key)` Returns the greatest key strictly less than the given key, or `null` if there is no such key.
`NavigableSet<K>` | `navigableKeySet()` Returns a `NavigableSet` view of the keys contained in this map.
`Map.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.
`Map.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.
`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`.
`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.
`SortedMap<K,V>` | `tailMap(K fromKey)` Returns a view of the portion of this map whose keys are greater than or equal to `fromKey`.
`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`.

Methods inherited from interface java.util.SortedMap
`comparator, entrySet, firstKey, keySet, lastKey, values`

Methods inherited from interface java.util.Map
`clear, containsKey, containsValue, equals, get, hashCode, isEmpty, put, putAll, remove, size`

Method Detail

### lowerEntry

    Map.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

### lowerKey

    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

### floorEntry

    Map.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

### floorKey

    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

### ceilingEntry

    Map.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

### ceilingKey

    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

### higherEntry

    Map.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

### higherKey

    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

### firstEntry

    Map.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

### lastEntry

    Map.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

### pollFirstEntry

    Map.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

### pollLastEntry

    Map.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

### descendingMap

    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

### navigableKeySet

    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

### descendingKeySet

    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

### subMap

    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 `fromExclusive` and `toExclusive` 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

### headMap

    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

### tailMap

    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

### subMap

    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)`.

  Specified by:
    `subMap` in interface `SortedMap<K,V>`
  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` - 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

### headMap

    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)`.

  Specified by:
    `headMap` in interface `SortedMap<K,V>`
  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` - 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

### tailMap

    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)`.

  Specified by:
    `tailMap` in interface `SortedMap<K,V>`
  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` - 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

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