Module java.base
Package java.util

Class TreeMap<K,​V>

  • Type Parameters:
    K - the type of keys maintained by this map
    V - the type of mapped values
    All Implemented Interfaces:
    Serializable, Cloneable, Map<K,​V>, NavigableMap<K,​V>, SortedMap<K,​V>
    public class TreeMap<K,​V>
extends AbstractMap<K,​V>
implements NavigableMap<K,​V>, Cloneable, Serializable
    A Red-Black tree based NavigableMap 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 implementation provides guaranteed log(n) time cost for the containsKey, get, put and remove operations. Algorithms are adaptations of those in Cormen, Leiserson, and Rivest's Introduction to Algorithms.

    Note that the ordering maintained by a tree map, like any sorted map, and whether or not an explicit comparator is provided, must be consistent with equals if this sorted map is to correctly implement the Map interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the Map interface is defined in terms of the equals operation, but a sorted map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal. The behavior of a sorted map is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Map interface.

    Note that this implementation is not synchronized. If multiple threads access a map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with an existing key is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedSortedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map: 

       SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

    The iterators returned by the iterator method of the collections returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

    Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

    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.)

    This class is a member of the Java Collections Framework.

    Since:
    1.2
    See Also:
    Map, HashMap, Hashtable, Comparable, Comparator, Collection, Serialized Form

    • Constructor Summary

      Constructors 
      Constructor Description
      TreeMap()
      Constructs a new, empty tree map, using the natural ordering of its keys.
      TreeMap​(Comparator<? super K> comparator)
      Constructs a new, empty tree map, ordered according to the given comparator.
      TreeMap​(Map<? extends K,​? extends V> m)
      Constructs a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys.
      TreeMap​(SortedMap<K,​? extends V> m)
      Constructs a new tree map containing the same mappings and using the same ordering as the specified sorted map.

    • Method Summary

      Modifier and Type Method Description
      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.
      void clear()
      Removes all of the mappings from this map.
      Object clone()
      Returns a shallow copy of this TreeMap instance.
      boolean containsKey​(Object key)
      Returns true if this map contains a mapping for the specified key.
      boolean containsValue​(Object value)
      Returns true if this map maps one or more keys to the specified value.
      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.
      Set<Map.Entry<K,​V>> entrySet()
      Returns a Set 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.
      K firstKey()
      Returns the first (lowest) key currently in this map.
      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.
      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.
      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.
      Set<K> keySet()
      Returns a Set view of the keys contained in this map.
      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.
      K lastKey()
      Returns the last (highest) key currently in this map.
      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.
      V put​(K key, V value)
      Associates the specified value with the specified key in this map.
      void putAll​(Map<? extends K,​? extends V> map)
      Copies all of the mappings from the specified map to this map.
      V remove​(Object key)
      Removes the mapping for this key from this TreeMap if present.
      int size()
      Returns the number of key-value mappings in this map.
      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.
      Collection<V> values()
      Returns a Collection view of the values contained in this map.

    • Constructor Detail

      • TreeMap

        public TreeMap()
        Constructs a new, empty tree map, using the natural ordering of its keys. All keys inserted into the map must implement the Comparable interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a ClassCastException for any keys k1 and k2 in the map. If the user attempts to put a key into the map that violates this constraint (for example, the user attempts to put a string key into a map whose keys are integers), the put(Object key, Object value) call will throw a ClassCastException.

      • TreeMap

        public TreeMap​(Comparator<? super K> comparator)
        Constructs a new, empty tree map, ordered according to the given comparator. All keys inserted into the map must be mutually comparable by the given comparator: comparator.compare(k1, k2) must not throw a ClassCastException for any keys k1 and k2 in the map. If the user attempts to put a key into the map that violates this constraint, the put(Object key, Object value) call will throw a ClassCastException.
        Parameters:
        comparator - the comparator that will be used to order this map. If null, the natural ordering of the keys will be used.

      • TreeMap

        public TreeMap​(Map<? extends K,​? extends V> m)
        Constructs a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys. All keys inserted into the new map must implement the Comparable interface. Furthermore, all such keys must be mutually comparable: k1.compareTo(k2) must not throw a ClassCastException for any keys k1 and k2 in the map. This method runs in n*log(n) time.
        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 is null

      • TreeMap

        public TreeMap​(SortedMap<K,​? extends V> m)
        Constructs a new tree map containing the same mappings and using the same ordering as the specified sorted map. This method runs in linear time.
        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 map is null

    • Method Detail

      • size

        public int size()
        Returns the number of key-value mappings in this map.
        Specified by:
        size in interface Map<K,​V>
        Overrides:
        size in class AbstractMap<K,​V>
        Returns:
        the number of key-value mappings in 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 and this map uses natural ordering, or its comparator does not permit null keys

      • containsValue

        public boolean containsValue​(Object value)
        Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations.
        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
        Since:
        1.2

      • 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.)

        A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

        Specified by:
        get in interface Map<K,​V>
        Overrides:
        get in class AbstractMap<K,​V>
        Parameters:
        key - the key whose associated value is to be returned
        Returns:
        the value to which the specified key is mapped, or null if this map contains 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 and this map uses natural ordering, or its comparator does not permit null keys

      • firstKey

        public K firstKey()
        Description copied from interface: SortedMap
        Returns the first (lowest) key currently in this map.
        Specified by:
        firstKey in interface SortedMap<K,​V>
        Returns:
        the first (lowest) key currently in this map
        Throws:
        NoSuchElementException - if this map is empty

      • lastKey

        public K lastKey()
        Description copied from interface: SortedMap
        Returns the last (highest) key currently in this map.
        Specified by:
        lastKey in interface SortedMap<K,​V>
        Returns:
        the last (highest) key currently in this map
        Throws:
        NoSuchElementException - if this map is empty

      • putAll

        public void putAll​(Map<? extends K,​? extends V> map)
        Copies all of the mappings from the specified map to this map. These mappings replace any mappings that this map had for any of the keys currently in the specified map.
        Specified by:
        putAll in interface Map<K,​V>
        Overrides:
        putAll in class AbstractMap<K,​V>
        Parameters:
        map - mappings to be stored in this map
        Throws:
        ClassCastException - if the class of a key or value in the specified map prevents it from being stored in this map
        NullPointerException - if the specified map is null or the specified map contains a null key and this map does not permit null keys

      • 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 key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with 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 uses natural ordering, or its comparator does not permit null keys

      • remove

        public V remove​(Object key)
        Removes the mapping for this key from this TreeMap 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 key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with 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 uses natural ordering, or its comparator does not permit null keys

      • clear

        public void clear()
        Removes all of the mappings from this map. The map will be empty after this call returns.
        Specified by:
        clear in interface Map<K,​V>
        Overrides:
        clear in class AbstractMap<K,​V>

      • clone

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

      • firstEntry

        public Map.Entry<K,​V> firstEntry()
        Description copied from interface: NavigableMap
        Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
        Specified by:
        firstEntry in interface NavigableMap<K,​V>
        Returns:
        an entry with the least key, or null if this map is empty
        Since:
        1.6

      • lastEntry

        public Map.Entry<K,​V> lastEntry()
        Description copied from interface: NavigableMap
        Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
        Specified by:
        lastEntry in interface NavigableMap<K,​V>
        Returns:
        an entry with the greatest key, or null if this map is empty
        Since:
        1.6

      • pollFirstEntry

        public Map.Entry<K,​V> pollFirstEntry()
        Description copied from interface: NavigableMap
        Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
        Specified by:
        pollFirstEntry in interface NavigableMap<K,​V>
        Returns:
        the removed first entry of this map, or null if this map is empty
        Since:
        1.6

      • pollLastEntry

        public Map.Entry<K,​V> pollLastEntry()
        Description copied from interface: NavigableMap
        Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
        Specified by:
        pollLastEntry in interface NavigableMap<K,​V>
        Returns:
        the removed last entry of this map, or null if this map is empty
        Since:
        1.6

      • lowerEntry

        public Map.Entry<K,​V> lowerEntry​(K key)
        Description copied from interface: NavigableMap
        Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
        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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • 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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • floorEntry

        public Map.Entry<K,​V> floorEntry​(K key)
        Description copied from interface: NavigableMap
        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.
        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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • 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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • ceilingEntry

        public Map.Entry<K,​V> ceilingEntry​(K key)
        Description copied from interface: NavigableMap
        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.
        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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • 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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • higherEntry

        public Map.Entry<K,​V> higherEntry​(K key)
        Description copied from interface: NavigableMap
        Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
        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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • 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 and this map uses natural ordering, or its comparator does not permit null keys
        Since:
        1.6

      • keySet

        public Set<K> keySet()
        Returns a Set view of the keys contained in this map.

        The set's iterator returns the keys in ascending order. The set's spliterator is late-binding, fail-fast, and additionally reports Spliterator.SORTED and Spliterator.ORDERED with an encounter order that is ascending key order. The spliterator's comparator (see Spliterator.getComparator()) is null if the tree map's comparator (see SortedMap.comparator()) is null. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the tree map's comparator.

        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.

        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 set view of the keys contained in this map

      • navigableKeySet

        public NavigableSet<K> navigableKeySet()
        Description copied from interface: NavigableMap
        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.
        Specified by:
        navigableKeySet in interface NavigableMap<K,​V>
        Returns:
        a navigable set view of the keys in this map
        Since:
        1.6

      • descendingKeySet

        public NavigableSet<K> descendingKeySet()
        Description copied from interface: NavigableMap
        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.
        Specified by:
        descendingKeySet in interface NavigableMap<K,​V>
        Returns:
        a reverse order navigable set view of the keys in this map
        Since:
        1.6

      • 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 collection's spliterator is late-binding, fail-fast, and additionally reports 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. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. 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.

        Specified by:
        values in interface Map<K,​V>
        Specified by:
        values in interface SortedMap<K,​V>
        Overrides:
        values in class AbstractMap<K,​V>
        Returns:
        a collection view of the values contained in this map

      • 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 is late-binding, fail-fast, and additionally reports 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. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) 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.

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

      • descendingMap

        public NavigableMap<K,​V> descendingMap()
        Description copied from interface: NavigableMap
        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.

        Specified by:
        descendingMap in interface NavigableMap<K,​V>
        Returns:
        a reverse order view of this map
        Since:
        1.6

      • subMap

        public NavigableMap<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 uses natural ordering, or its comparator 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
        Since:
        1.6

      • headMap

        public NavigableMap<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 uses natural ordering, or its comparator does not permit null keys
        IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range
        Since:
        1.6

      • tailMap

        public NavigableMap<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 uses natural ordering, or its comparator does not permit null keys
        IllegalArgumentException - if this map itself has a restricted range, and fromKey lies outside the bounds of the range
        Since:
        1.6

      • subMap

        public SortedMap<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 uses natural ordering, or its comparator 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

        public SortedMap<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 uses natural ordering, or its comparator does not permit null keys
        IllegalArgumentException - if this map itself has a restricted range, and toKey lies outside the bounds of the range

      • tailMap

        public SortedMap<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 uses natural ordering, or its comparator does not permit null keys
        IllegalArgumentException - if this map itself has a restricted range, and fromKey lies outside the bounds of the range