ConcurrentNavigableMap (Java Platform SE 8 )
Keywords: java.util.concurrent.ConcurrentNavigableMap interface
Date: 2026-03-16

compact1, compact2, compact3
java.util.concurrent

## Interface ConcurrentNavigableMap<K,V>

- Type Parameters:
    `K` - the type of keys maintained by this map
    `V` - the type of mapped values
  All Superinterfaces:
    ConcurrentMap<K,V>, Map<K,V>, NavigableMap<K,V>, SortedMap<K,V>
  All Known Implementing Classes:
    ConcurrentSkipListMap

      public interface ConcurrentNavigableMap<K,V>
      extends ConcurrentMap<K,V>, NavigableMap<K,V>

  A `ConcurrentMap` supporting `NavigableMap` operations, and recursively so for its navigable sub-maps.

  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

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `NavigableSet<K>` | `descendingKeySet()` Returns a reverse order `NavigableSet` view of the keys contained in this map.
    `ConcurrentNavigableMap<K,V>` | `descendingMap()` Returns a reverse order view of the mappings contained in this map.
    `ConcurrentNavigableMap<K,V>` | `headMap(K toKey)` Returns a view of the portion of this map whose keys are strictly less than `toKey`.
    `ConcurrentNavigableMap<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`.
    `NavigableSet<K>` | `keySet()` Returns a `NavigableSet` view of the keys contained in this map.
    `NavigableSet<K>` | `navigableKeySet()` Returns a `NavigableSet` view of the keys contained in this map.
    `ConcurrentNavigableMap<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`.
    `ConcurrentNavigableMap<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.
    `ConcurrentNavigableMap<K,V>` | `tailMap(K fromKey)` Returns a view of the portion of this map whose keys are greater than or equal to `fromKey`.
    `ConcurrentNavigableMap<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.concurrent.ConcurrentMap

      `compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll`

    - ### Methods inherited from interface java.util.NavigableMap

      `ceilingEntry, ceilingKey, firstEntry, floorEntry, floorKey, higherEntry, higherKey, lastEntry, lowerEntry, lowerKey, pollFirstEntry, pollLastEntry`

    - ### Methods inherited from interface java.util.SortedMap

      `comparator, entrySet, firstKey, lastKey, values`

    - ### Methods inherited from interface java.util.Map

      `clear, containsKey, containsValue, equals, get, hashCode, isEmpty, put, putAll, remove, size`

- - ### Method Detail

    - #### subMap

          ConcurrentNavigableMap<K,V> subMap(K fromKey,
                                             boolean fromInclusive,
                                             K toKey,
                                             boolean toInclusive)

      Description copied from interface: `NavigableMap`
      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.

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

          ConcurrentNavigableMap<K,V> headMap(K toKey,
                                              boolean inclusive)

      Description copied from interface: `NavigableMap`
      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.

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

          ConcurrentNavigableMap<K,V> tailMap(K fromKey,
                                              boolean inclusive)

      Description copied from interface: `NavigableMap`
      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.

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

          ConcurrentNavigableMap<K,V> subMap(K fromKey,
                                             K toKey)

      Description copied from interface: `NavigableMap`
      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 `NavigableMap<K,V>`
      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

          ConcurrentNavigableMap<K,V> headMap(K toKey)

      Description copied from interface: `NavigableMap`
      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 `NavigableMap<K,V>`
      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

          ConcurrentNavigableMap<K,V> tailMap(K fromKey)

      Description copied from interface: `NavigableMap`
      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 `NavigableMap<K,V>`
      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

    - #### descendingMap

          ConcurrentNavigableMap<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.

      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`.

      Specified by:
        `descendingMap` in interface `NavigableMap<K,V>`
      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. 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.

      The view's iterators and spliterators are weakly consistent.

      Specified by:
        `navigableKeySet` in interface `NavigableMap<K,V>`
      Returns:
        a navigable set view of the keys in this map

    - #### keySet

          NavigableSet<K> keySet()

      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. 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.

      The view's iterators and spliterators are weakly consistent.

      This method is equivalent to method `navigableKeySet`.

      Specified by:
        `keySet` in interface `Map<K,V>`
      Specified by:
        `keySet` in interface `SortedMap<K,V>`
      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. 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.

      The view's iterators and spliterators are weakly consistent.

      Specified by:
        `descendingKeySet` in interface `NavigableMap<K,V>`
      Returns:
        a reverse order navigable set view of the keys in this map

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