ConcurrentNavigableMap (Java Platform SE 7 ) (original) (raw)
- Type Parameters:
K- the type of keys maintained by this mapV- 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>
Since:
1.6
Nested Class Summary
* ### Nested classes/interfaces inherited from interface java.util.[Map](../../../java/util/Map.html "interface in java.util") `[Map.Entry](../../../java/util/Map.Entry.html "interface in java.util")<[K](../../../java/util/Map.Entry.html "type parameter in Map.Entry"),[V](../../../java/util/Map.Entry.html "type parameter in Map.Entry")>`Method Summary
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 fromfromKey to toKey. ConcurrentNavigableMap<K,V> subMap(K fromKey,K toKey) Returns a view of the portion of this map whose keys range fromfromKey, 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](../../../java/util/concurrent/ConcurrentMap.html "interface in java.util.concurrent") `[putIfAbsent](../../../java/util/concurrent/ConcurrentMap.html#putIfAbsent%28K,%20V%29), [remove](../../../java/util/concurrent/ConcurrentMap.html#remove%28java.lang.Object,%20java.lang.Object%29), [replace](../../../java/util/concurrent/ConcurrentMap.html#replace%28K,%20V%29), [replace](../../../java/util/concurrent/ConcurrentMap.html#replace%28K,%20V,%20V%29)` * ### Methods inherited from interface java.util.[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util") `[ceilingEntry](../../../java/util/NavigableMap.html#ceilingEntry%28K%29), [ceilingKey](../../../java/util/NavigableMap.html#ceilingKey%28K%29), [firstEntry](../../../java/util/NavigableMap.html#firstEntry%28%29), [floorEntry](../../../java/util/NavigableMap.html#floorEntry%28K%29), [floorKey](../../../java/util/NavigableMap.html#floorKey%28K%29), [higherEntry](../../../java/util/NavigableMap.html#higherEntry%28K%29), [higherKey](../../../java/util/NavigableMap.html#higherKey%28K%29), [lastEntry](../../../java/util/NavigableMap.html#lastEntry%28%29), [lowerEntry](../../../java/util/NavigableMap.html#lowerEntry%28K%29), [lowerKey](../../../java/util/NavigableMap.html#lowerKey%28K%29), [pollFirstEntry](../../../java/util/NavigableMap.html#pollFirstEntry%28%29), [pollLastEntry](../../../java/util/NavigableMap.html#pollLastEntry%28%29)` * ### Methods inherited from interface java.util.[SortedMap](../../../java/util/SortedMap.html "interface in java.util") `[comparator](../../../java/util/SortedMap.html#comparator%28%29), [entrySet](../../../java/util/SortedMap.html#entrySet%28%29), [firstKey](../../../java/util/SortedMap.html#firstKey%28%29), [lastKey](../../../java/util/SortedMap.html#lastKey%28%29), [values](../../../java/util/SortedMap.html#values%28%29)` * ### Methods inherited from interface java.util.[Map](../../../java/util/Map.html "interface in java.util") `[clear](../../../java/util/Map.html#clear%28%29), [containsKey](../../../java/util/Map.html#containsKey%28java.lang.Object%29), [containsValue](../../../java/util/Map.html#containsValue%28java.lang.Object%29), [equals](../../../java/util/Map.html#equals%28java.lang.Object%29), [get](../../../java/util/Map.html#get%28java.lang.Object%29), [hashCode](../../../java/util/Map.html#hashCode%28%29), [isEmpty](../../../java/util/Map.html#isEmpty%28%29), [put](../../../java/util/Map.html#put%28K,%20V%29), [putAll](../../../java/util/Map.html#putAll%28java.util.Map%29), [remove](../../../java/util/Map.html#remove%28java.lang.Object%29), [size](../../../java/util/Map.html#size%28%29)`Method Detail
* #### subMap [ConcurrentNavigableMap](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> subMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") fromKey, boolean fromInclusive, [K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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. **Specified by:** `[subMap](../../../java/util/NavigableMap.html#subMap%28K,%20boolean,%20K,%20boolean%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- 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](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `fromKey` or `toKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- 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](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> headMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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. **Specified by:** `[headMap](../../../java/util/NavigableMap.html#headMap%28K,%20boolean%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- if `toKey` is not compatible with this map's comparator (or, if the map has no comparator, if `toKey` does not implement [Comparable](../../../java/lang/Comparable.html "interface in java.lang")). Implementations may, but are not required to, throw this exception if `toKey` cannot be compared to keys currently in the map. `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `toKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if this map itself has a restricted range, and `toKey` lies outside the bounds of the range * #### tailMap [ConcurrentNavigableMap](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> tailMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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. **Specified by:** `[tailMap](../../../java/util/NavigableMap.html#tailMap%28K,%20boolean%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- if `fromKey` is not compatible with this map's comparator (or, if the map has no comparator, if `fromKey` does not implement [Comparable](../../../java/lang/Comparable.html "interface in java.lang")). Implementations may, but are not required to, throw this exception if `fromKey` cannot be compared to keys currently in the map. `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `fromKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if this map itself has a restricted range, and `fromKey` lies outside the bounds of the range * #### subMap [ConcurrentNavigableMap](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> subMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") fromKey, [K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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](../../../java/util/NavigableMap.html#subMap%28K,%20K%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` **Specified by:** `[subMap](../../../java/util/SortedMap.html#subMap%28K,%20K%29)` in interface `[SortedMap](../../../java/util/SortedMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- 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](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `fromKey` or `toKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- 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](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> headMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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](../../../java/util/NavigableMap.html#headMap%28K%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` **Specified by:** `[headMap](../../../java/util/SortedMap.html#headMap%28K%29)` in interface `[SortedMap](../../../java/util/SortedMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- if `toKey` is not compatible with this map's comparator (or, if the map has no comparator, if `toKey` does not implement [Comparable](../../../java/lang/Comparable.html "interface in java.lang")). Implementations may, but are not required to, throw this exception if `toKey` cannot be compared to keys currently in the map. `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `toKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if this map itself has a restricted range, and `toKey` lies outside the bounds of the range * #### tailMap [ConcurrentNavigableMap](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> tailMap([K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap") 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](../../../java/util/NavigableMap.html#tailMap%28K%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` **Specified by:** `[tailMap](../../../java/util/SortedMap.html#tailMap%28K%29)` in interface `[SortedMap](../../../java/util/SortedMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` 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](../../../java/lang/ClassCastException.html "class in java.lang")` \- if `fromKey` is not compatible with this map's comparator (or, if the map has no comparator, if `fromKey` does not implement [Comparable](../../../java/lang/Comparable.html "interface in java.lang")). Implementations may, but are not required to, throw this exception if `fromKey` cannot be compared to keys currently in the map. `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if `fromKey` is null and this map does not permit null keys `[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if this map itself has a restricted range, and `fromKey` lies outside the bounds of the range * #### descendingMap [ConcurrentNavigableMap](../../../java/util/concurrent/ConcurrentNavigableMap.html "interface in java.util.concurrent")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> 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](../../../java/util/Collections.html#reverseOrder%28java.util.Comparator%29)(comparator()). The expression `m.descendingMap().descendingMap()` returns a view of `m` essentially equivalent to `m`. **Specified by:** `[descendingMap](../../../java/util/NavigableMap.html#descendingMap%28%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` Returns: a reverse order view of this map * #### navigableKeySet [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> navigableKeySet() Returns a [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util") 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 `iterator` is a "weakly consistent" iterator that will never throw [ConcurrentModificationException](../../../java/util/ConcurrentModificationException.html "class in java.util"), and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction. **Specified by:** `[navigableKeySet](../../../java/util/NavigableMap.html#navigableKeySet%28%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` Returns: a navigable set view of the keys in this map * #### keySet [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> keySet() Returns a [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util") 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 `iterator` is a "weakly consistent" iterator that will never throw [ConcurrentModificationException](../../../java/util/ConcurrentModificationException.html "class in java.util"), and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction. This method is equivalent to method `navigableKeySet`. **Specified by:** `[keySet](../../../java/util/Map.html#keySet%28%29)` in interface `[Map](../../../java/util/Map.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` **Specified by:** `[keySet](../../../java/util/SortedMap.html#keySet%28%29)` in interface `[SortedMap](../../../java/util/SortedMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` Returns: a navigable set view of the keys in this map * #### descendingKeySet [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")> descendingKeySet() Returns a reverse order [NavigableSet](../../../java/util/NavigableSet.html "interface in java.util") 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 `iterator` is a "weakly consistent" iterator that will never throw [ConcurrentModificationException](../../../java/util/ConcurrentModificationException.html "class in java.util"), and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction. **Specified by:** `[descendingKeySet](../../../java/util/NavigableMap.html#descendingKeySet%28%29)` in interface `[NavigableMap](../../../java/util/NavigableMap.html "interface in java.util")<[K](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap"),[V](../../../java/util/concurrent/ConcurrentNavigableMap.html "type parameter in ConcurrentNavigableMap")>` Returns: a reverse order navigable set view of the keys in this map
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