Module java.base

Class ConcurrentSkipListMap<K,V>

  • Type Parameters:
    K - the type of keys maintained by this map
    V - the type of mapped values
    All Implemented Interfaces:
    Serializable, Cloneable, ConcurrentMap<K,V>, ConcurrentNavigableMap<K,V>, Map<K,V>, NavigableMap<K,V>, SortedMap<K,V>


    public class ConcurrentSkipListMap<K,V>
    extends AbstractMap<K,V>
    implements ConcurrentNavigableMap<K,V>, Cloneable, Serializable
    A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

    This class implements a concurrent variant of SkipLists providing expected average log(n) time cost for the containsKey, get, put and remove operations and their variants. Insertion, removal, update, and access operations safely execute concurrently by multiple threads.

    Iterators and spliterators are weakly consistent.

    Ascending key ordered views and their iterators are faster than descending ones.

    All Map.Entry pairs returned by methods in this class and its views represent snapshots of mappings at the time they were produced. They do not support the Entry.setValue method. (Note however that it is possible to change mappings in the associated map using put, putIfAbsent, or replace, depending on exactly which effect you need.)

    Beware that bulk operations putAll, equals, toArray, containsValue, and clear are not guaranteed to be performed atomically. For example, an iterator operating concurrently with a putAll operation might view only some of the added elements.

    This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces. Like most other concurrent collections, this class does not permit the use of null keys or values because some null return values cannot be reliably distinguished from the absence of elements.

    This class is a member of the Java Collections Framework.

    Since:
    1.6
    Author:
    Doug Lea
    See Also:
    Serialized Form
    • Constructor Detail

      • ConcurrentSkipListMap

        public ConcurrentSkipListMap​()
        Constructs a new, empty map, sorted according to the natural ordering of the keys.
      • ConcurrentSkipListMap

        public ConcurrentSkipListMap​(Comparator<? super K> comparator)
        Constructs a new, empty map, sorted according to the specified comparator.
        Parameters:
        comparator - the comparator that will be used to order this map. If null, the natural ordering of the keys will be used.
      • ConcurrentSkipListMap

        public ConcurrentSkipListMap​(Map<? extends K,? extends V> m)
        Constructs a new map containing the same mappings as the given map, sorted according to the natural ordering of the keys.
        Parameters:
        m - the map whose mappings are to be placed in this map
        Throws:
        ClassCastException - if the keys in m are not Comparable, or are not mutually comparable
        NullPointerException - if the specified map or any of its keys or values are null
      • ConcurrentSkipListMap

        public ConcurrentSkipListMap​(SortedMap<K,? extends V> m)
        Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.
        Parameters:
        m - the sorted map whose mappings are to be placed in this map, and whose comparator is to be used to sort this map
        Throws:
        NullPointerException - if the specified sorted map or any of its keys or values are null
    • Method Detail

      • clone

        public ConcurrentSkipListMap<K,V> clone​()
        Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.)
        Overrides:
        clone in class AbstractMap<K,V>
        Returns:
        a shallow copy of this map
      • containsKey

        public boolean containsKey​(Object key)
        Returns true if this map contains a mapping for the specified key.
        Specified by:
        containsKey in interface Map<K,V>
        Overrides:
        containsKey in class AbstractMap<K,V>
        Parameters:
        key - key whose presence in this map is to be tested
        Returns:
        true if this map contains a mapping for the specified key
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key is null
      • get

        public 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.

        More formally, if this map contains a mapping from a key k to a value v such that key compares equal to k according to the map's ordering, then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

        Specified by:
        get in interface Map<K,V>
        Overrides:
        get in class AbstractMap<K,V>
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key is null
      • getOrDefault

        public V getOrDefault​(Object key,
                              V defaultValue)
        Returns the value to which the specified key is mapped, or the given defaultValue if this map contains no mapping for the key.
        Specified by:
        getOrDefault in interface ConcurrentMap<K,V>
        Specified by:
        getOrDefault in interface Map<K,V>
        Parameters:
        key - the key
        defaultValue - the value to return if this map contains no mapping for the given key
        Returns:
        the mapping for the key, if present; else the defaultValue
        Throws:
        NullPointerException - if the specified key is null
        Since:
        1.8
      • put

        public V put​(K key,
                     V value)
        Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
        Specified by:
        put in interface Map<K,V>
        Overrides:
        put in class AbstractMap<K,V>
        Parameters:
        key - key with which the specified value is to be associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key or value is null
      • remove

        public V remove​(Object key)
        Removes the mapping for the specified key from this map if present.
        Specified by:
        remove in interface Map<K,V>
        Overrides:
        remove in class AbstractMap<K,V>
        Parameters:
        key - key for which mapping should be removed
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key is null
      • containsValue

        public boolean containsValue​(Object value)
        Returns true if this map maps one or more keys to the specified value. This operation requires time linear in the map size. Additionally, it is possible for the map to change during execution of this method, in which case the returned result may be inaccurate.
        Specified by:
        containsValue in interface Map<K,V>
        Overrides:
        containsValue in class AbstractMap<K,V>
        Parameters:
        value - value whose presence in this map is to be tested
        Returns:
        true if a mapping to value exists; false otherwise
        Throws:
        NullPointerException - if the specified value is null
      • clear

        public void clear​()
        Removes all of the mappings from this map.
        Specified by:
        clear in interface Map<K,V>
        Overrides:
        clear in class AbstractMap<K,V>
      • computeIfAbsent

        public V computeIfAbsent​(K key,
                                 Function<? super K,? extends V> mappingFunction)
        If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless null. The function is NOT guaranteed to be applied once atomically only if the value is not present.
        Specified by:
        computeIfAbsent in interface ConcurrentMap<K,V>
        Specified by:
        computeIfAbsent in interface Map<K,V>
        Parameters:
        key - key with which the specified value is to be associated
        mappingFunction - the function to compute a value
        Returns:
        the current (existing or computed) value associated with the specified key, or null if the computed value is null
        Throws:
        NullPointerException - if the specified key is null or the mappingFunction is null
        Since:
        1.8
      • computeIfPresent

        public V computeIfPresent​(K key,
                                  BiFunction<? super K,? super V,? extends V> remappingFunction)
        If the value for the specified key is present, attempts to compute a new mapping given the key and its current mapped value. The function is NOT guaranteed to be applied once atomically.
        Specified by:
        computeIfPresent in interface ConcurrentMap<K,V>
        Specified by:
        computeIfPresent in interface Map<K,V>
        Parameters:
        key - key with which a value may be associated
        remappingFunction - the function to compute a value
        Returns:
        the new value associated with the specified key, or null if none
        Throws:
        NullPointerException - if the specified key is null or the remappingFunction is null
        Since:
        1.8
      • compute

        public 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). The function is NOT guaranteed to be applied once atomically.
        Specified by:
        compute in interface ConcurrentMap<K,V>
        Specified by:
        compute in interface Map<K,V>
        Parameters:
        key - key with which the specified value is to be associated
        remappingFunction - the function to compute a value
        Returns:
        the new value associated with the specified key, or null if none
        Throws:
        NullPointerException - if the specified key is null or the remappingFunction is null
        Since:
        1.8
      • merge

        public 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, associates it with the given value. Otherwise, replaces the value with the results of the given remapping function, or removes if null. The function is NOT guaranteed to be applied once atomically.
        Specified by:
        merge in interface ConcurrentMap<K,V>
        Specified by:
        merge in interface Map<K,V>
        Parameters:
        key - key with which the specified value is to be associated
        value - the value to use if absent
        remappingFunction - the function to recompute a value if present
        Returns:
        the new value associated with the specified key, or null if none
        Throws:
        NullPointerException - if the specified key or value is null or the remappingFunction is null
        Since:
        1.8
      • keySet

        public 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's spliterator additionally reports Spliterator.CONCURRENT, Spliterator.NONNULL, Spliterator.SORTED and Spliterator.ORDERED, with an encounter order that is ascending key order.

        The spliterator's comparator is null if the map's comparator is null. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the map's comparator.

        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 ConcurrentNavigableMap<K,V>
        Specified by:
        keySet in interface Map<K,V>
        Specified by:
        keySet in interface SortedMap<K,V>
        Overrides:
        keySet in class AbstractMap<K,V>
        Returns:
        a navigable set view of the keys in this map
      • navigableKeySet

        public NavigableSet<K> navigableKeySet​()
        Description copied from interface: ConcurrentNavigableMap
        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 ConcurrentNavigableMap<K,V>
        Specified by:
        navigableKeySet in interface NavigableMap<K,V>
        Returns:
        a navigable set view of the keys in this map
      • values

        public Collection<V> values​()
        Returns a Collection view of the values contained in this map.

        The collection's iterator returns the values in ascending order of the corresponding keys. The collections's spliterator additionally reports Spliterator.CONCURRENT, Spliterator.NONNULL and Spliterator.ORDERED, with an encounter order that is ascending order of the corresponding keys.

        The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.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:
        values in interface Map<K,V>
        Specified by:
        values in interface SortedMap<K,V>
        Overrides:
        values in class AbstractMap<K,V>
      • entrySet

        public Set<Map.Entry<K,V>> entrySet​()
        Returns a Set view of the mappings contained in this map.

        The set's iterator returns the entries in ascending key order. The set's spliterator additionally reports Spliterator.CONCURRENT, Spliterator.NONNULL, Spliterator.SORTED and Spliterator.ORDERED, with an encounter order that is ascending key 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.

        The Map.Entry elements traversed by the iterator or spliterator do not support the setValue operation.

        Specified by:
        entrySet in interface Map<K,V>
        Specified by:
        entrySet in interface SortedMap<K,V>
        Specified by:
        entrySet in class AbstractMap<K,V>
        Returns:
        a set view of the mappings contained in this map, sorted in ascending key order
      • descendingMap

        public ConcurrentNavigableMap<K,V> descendingMap​()
        Description copied from interface: ConcurrentNavigableMap
        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 ConcurrentNavigableMap<K,V>
        Specified by:
        descendingMap in interface NavigableMap<K,V>
        Returns:
        a reverse order view of this map
      • descendingKeySet

        public NavigableSet<K> descendingKeySet​()
        Description copied from interface: ConcurrentNavigableMap
        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 ConcurrentNavigableMap<K,V>
        Specified by:
        descendingKeySet in interface NavigableMap<K,V>
        Returns:
        a reverse order navigable set view of the keys in this map
      • equals

        public boolean equals​(Object o)
        Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This operation may return misleading results if either map is concurrently modified during execution of this method.
        Specified by:
        equals in interface Map<K,V>
        Overrides:
        equals in class AbstractMap<K,V>
        Parameters:
        o - object to be compared for equality with this map
        Returns:
        true if the specified object is equal to this map
      • putIfAbsent

        public V putIfAbsent​(K key,
                             V value)
        If the specified key is not already associated with a value, associates it with the given value. This is equivalent to, for this map:
         
         if (!map.containsKey(key))
           return map.put(key, value);
         else
           return map.get(key);
        except that the action is performed atomically.
        Specified by:
        putIfAbsent in interface ConcurrentMap<K,V>
        Specified by:
        putIfAbsent in interface Map<K,V>
        Parameters:
        key - key with which the specified value is to be associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key or value is null
      • remove

        public boolean remove​(Object key,
                              Object value)
        Removes the entry for a key only if currently mapped to a given value. This is equivalent to, for this map:
         
         if (map.containsKey(key)
             && Objects.equals(map.get(key), value)) {
           map.remove(key);
           return true;
         } else {
           return false;
         }
        except that the action is performed atomically.
        Specified by:
        remove in interface ConcurrentMap<K,V>
        Specified by:
        remove in interface Map<K,V>
        Parameters:
        key - key with which the specified value is associated
        value - value expected to be associated with the specified key
        Returns:
        true if the value was removed
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key is null
      • replace

        public boolean replace​(K key,
                               V oldValue,
                               V newValue)
        Replaces the entry for a key only if currently mapped to a given value. This is equivalent to, for this map:
         
         if (map.containsKey(key)
             && Objects.equals(map.get(key), oldValue)) {
           map.put(key, newValue);
           return true;
         } else {
           return false;
         }
        except that the action is performed atomically.
        Specified by:
        replace in interface ConcurrentMap<K,V>
        Specified by:
        replace in interface Map<K,V>
        Parameters:
        key - key with which the specified value is associated
        oldValue - value expected to be associated with the specified key
        newValue - value to be associated with the specified key
        Returns:
        true if the value was replaced
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if any of the arguments are null
      • replace

        public V replace​(K key,
                         V value)
        Replaces the entry for a key only if currently mapped to some value. This is equivalent to, for this map:
         
         if (map.containsKey(key))
           return map.put(key, value);
         else
           return null;
        except that the action is performed atomically.
        Specified by:
        replace in interface ConcurrentMap<K,V>
        Specified by:
        replace in interface Map<K,V>
        Parameters:
        key - key with which the specified value is associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        ClassCastException - if the specified key cannot be compared with the keys currently in the map
        NullPointerException - if the specified key or value is null
      • subMap

        public 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 ConcurrentNavigableMap<K,V>
        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
        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

        public 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 ConcurrentNavigableMap<K,V>
        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
        IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range
      • tailMap

        public 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 ConcurrentNavigableMap<K,V>
        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
        IllegalArgumentException - if this map itself has a restricted range, and fromKey lies outside the bounds of the range
      • lowerEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        lowerEntry in interface NavigableMap<K,V>
        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
      • lowerKey

        public K lowerKey​(K key)
        Description copied from interface: NavigableMap
        Returns the greatest key strictly less than the given key, or null if there is no such key.
        Specified by:
        lowerKey in interface NavigableMap<K,V>
        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
      • floorEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        floorEntry in interface NavigableMap<K,V>
        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
      • floorKey

        public K floorKey​(K key)
        Description copied from interface: NavigableMap
        Returns the greatest key less than or equal to the given key, or null if there is no such key.
        Specified by:
        floorKey in interface NavigableMap<K,V>
        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
      • ceilingEntry

        public 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 entry. The returned entry does not support the Entry.setValue method.
        Specified by:
        ceilingEntry in interface NavigableMap<K,V>
        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
      • ceilingKey

        public K ceilingKey​(K key)
        Description copied from interface: NavigableMap
        Returns the least key greater than or equal to the given key, or null if there is no such key.
        Specified by:
        ceilingKey in interface NavigableMap<K,V>
        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
      • higherEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        higherEntry in interface NavigableMap<K,V>
        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
      • higherKey

        public K higherKey​(K key)
        Description copied from interface: NavigableMap
        Returns the least key strictly greater than the given key, or null if there is no such key.
        Specified by:
        higherKey in interface NavigableMap<K,V>
        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
      • firstEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        firstEntry in interface NavigableMap<K,V>
        Returns:
        an entry with the least key, or null if this map is empty
      • lastEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        lastEntry in interface NavigableMap<K,V>
        Returns:
        an entry with the greatest key, or null if this map is empty
      • pollFirstEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        pollFirstEntry in interface NavigableMap<K,V>
        Returns:
        the removed first entry of this map, or null if this map is empty
      • pollLastEntry

        public 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. The returned entry does not support the Entry.setValue method.
        Specified by:
        pollLastEntry in interface NavigableMap<K,V>
        Returns:
        the removed last entry of this map, or null if this map is empty