Java The Complete Reference, Seventh Edition

466 Part II: The Java Library

The NavigableMap Interface

TheNavigableMapinterface was added by Java SE 6. It extendsSortedMapand declares

the behavior of a map that supports the retrieval of entries based on the closest match to a

given key or keys.NavigableMapis a generic interface that has this declaration:

interface NavigableMap<K,V>

Here,Kspecifies the type of the keys, andVspecifies the type of the values associated with

the keys. In addition to the methods that it inherits fromSortedMap,NavigableMapadds

those summarized in Table 17-12. Several methods throw aClassCastExceptionwhen

an object is incompatible with the keys in the map. ANullPointerExceptionis thrown

if an attempt is made to use anullobject andnullkeys are not allowed in the set. An

IllegalArgumentExceptionis thrown if an invalid argument is used.

Method Description

Comparator<? super K> comparator( ) Returns the invoking sor ted map’s comparator. If natural

ordering is used for the invoking map,nullis returned.

K firstKey( ) Returns the first key in the invoking map.

Sor tedMap<K, V> headMap(Kend) Returns a sor ted map for those map entries with keys that are

less thanend.

K lastKey( ) Returns the last key in the invoking map.

Sor tedMap<K, V> subMap(Kstar t, Kend) Returns a map containing those entries with keys that are

greater than or equal tostar tand less thanend.

Sor tedMap<K, V> tailMap(Kstar t) Returns a map containing those entries with keys that are

greater than or equal tostar t.

TABLE 17-11 The Methods Defined bySortedMap

Method Description

Map.Entr y<K,V> ceilingEntr y(Kobj) Searches the map for the smallest keyksuch thatk>=obj. If such a key

is found, its entr y is returned. Other wise,nullis returned.

K ceilingKey(Kobj) Searches the map for the smallest keyksuch thatk>=obj. If such a key

is found, it is returned. Other wise,nullis returned.

NavigableSet<K> descendingKeySet( ) Returns aNavigableSetthat contains the keys in the invoking map in

reverse order. Thus, it returns a reverse set-view of the keys. The

resulting set is backed by the map.

NavigableMap<K,V> descendingMap( ) Returns aNavigableMapthat is the reverse of the invoking map. The

resulting map is backed by the invoking map.

Map.Entr y<K,V> firstEntr y( ) Returns the first entr y in the map. This is the entr y with the least key.

Map.Entr y<K,V> floorEntr y(Kobj) Searches the map for the largest keyksuch thatk<=obj. If such a key

is found, its entr y is returned. Other wise,nullis returned.

K floorKey(Kobj) Searches the map for the largest keyksuch thatk<=obj. If such a key

is found, it is returned. Other wise,nullis returned.

NavigableMap<K,V>

headMap(KupperBound, booleanincl)

Returns aNavigableMapthat includes all entries from the invoking map

that have keys that are less thanupperBound. Ifinclistrue, then an

element equal toupperBoundis included. The resulting map is backed by

the invoking map.

Map.Entr y<K,V> higherEntr y(Kobj) Searches the set for the largest keyksuch thatk>obj. If such a key is

found, its entr y is returned. Other wise,nullis returned.

TABLE 17-12 The Methods defined byNavigableMap