A
SortedMap
extended with navigation methods returning the
closest matches for given search targets. Methods
lowerEntry
,
floorEntry
,
ceilingEntry
,
and
higherEntry
return
Map.Entry
objects
associated with keys respectively less than, less than or equal,
greater than or equal, and greater than a given key, returning
null
if there is no such key. Similarly, methods
lowerKey
,
floorKey
,
ceilingKey
, and
higherKey
return only the associated keys. All of these
methods are designed for locating, not traversing entries.
A NavigableMap
may be accessed and traversed in either
ascending or descending key order. The descendingMap
method returns a view of the map with the senses of all relational
and directional methods inverted. The performance of ascending
operations and views is likely to be faster than that of descending
ones. Methods subMap
, headMap
,
and tailMap
differ from the like-named SortedMap
methods in accepting additional arguments describing
whether lower and upper bounds are inclusive versus exclusive.
Submaps of any NavigableMap
must implement the NavigableMap
interface.
This interface additionally defines methods firstEntry
,
pollFirstEntry
, lastEntry
, and
pollLastEntry
that return and/or remove the least and
greatest mappings, if any exist, else returning null
.
Implementations of entry-returning methods are expected to
return Map.Entry
pairs representing snapshots of mappings
at the time they were produced, and thus generally do not
support the optional Entry.setValue
method. Note however
that it is possible to change mappings in the associated map using
method put
.
Methods
subMap(K, K)
,
headMap(K)
, and
tailMap(K)
are specified to return SortedMap
to allow existing
implementations of SortedMap
to be compatibly retrofitted to
implement NavigableMap
, but extensions and implementations
of this interface are encouraged to override these methods to return
NavigableMap
. Similarly,
SortedMap.keySet()
can be overriden to return NavigableSet
.
This interface is a member of the
Java Collections Framework.