SortedMap
public
interface
SortedMap
implements
SequencedMap<K, V>,
Map<K, V>
java.util.SortedMap<K, V> |
A Map
that further provides a total ordering on its keys.
The map is ordered according to the ordering of its keys, or by a Comparator
typically
provided at sorted map creation time. This order is reflected when
iterating over the sorted map's collection views (returned by the
entrySet
, keySet
and values
methods).
Several additional operations are provided to take advantage of the
ordering. (This interface is the map analogue of SortedSet
.)
All keys inserted into a sorted map must implement the Comparable
interface (or be accepted by the specified comparator). Furthermore, all
such keys must be mutually comparable: k1.compareTo(k2)
(or
comparator.compare(k1, k2)
) must not throw a
ClassCastException
for any keys k1
and k2
in
the sorted map. Attempts to violate this restriction will cause the
offending method or constructor invocation to throw a
ClassCastException
.
Note that the ordering maintained by a sorted map (whether or not an
explicit comparator is provided) must be consistent with equals if
the sorted map is to correctly implement the Map
interface. (See
the Comparable
interface or Comparator
interface 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 tree map is well-defined even if its
ordering is inconsistent with equals; it just fails to obey the general
contract of the Map
interface.
All general-purpose sorted map implementation classes should provide four "standard" constructors. It is not possible to enforce this recommendation though as required constructors cannot be specified by interfaces. The expected "standard" constructors for all sorted map implementations are:
- A void (no arguments) constructor, which creates an empty sorted map sorted according to the natural ordering of its keys.
- A constructor with a single argument of type
Comparator
, which creates an empty sorted map sorted according to the specified comparator. - A constructor with a single argument of type
Map
, which creates a new map with the same key-value mappings as its argument, sorted according to the keys' natural ordering. - A constructor with a single argument of type
SortedMap
, which creates a new sorted map with the same key-value mappings and the same ordering as the input sorted map.
Note: several methods return submaps with restricted key
ranges. Such ranges are half-open, that is, they include their low
endpoint but not their high endpoint (where applicable). If you need a
closed range (which includes both endpoints), and the key type
allows for calculation of the successor of a given key, merely request
the subrange from lowEndpoint
to
successor(highEndpoint)
. For example, suppose that m
is a map whose keys are strings. The following idiom obtains a view
containing all of the key-value mappings in m
whose keys are
between low
and high
, inclusive:
SortedMap<String, V> sub = m.subMap(low, high+"\0");
m
whose keys
are between low
and high
, exclusive:SortedMap<String, V> sub = m.subMap(low+"\0", high);
This interface is a member of the Java Collections Framework.
Summary
Public methods | |
---|---|
abstract
Comparator<? super K>
|
comparator()
Returns the comparator used to order the keys in this map, or
|
abstract
Set<Entry<K, V>>
|
entrySet()
Returns a |
abstract
K
|
firstKey()
Returns the first (lowest) key currently in this map. |
abstract
SortedMap<K, V>
|
headMap(K toKey)
Returns a view of the portion of this map whose keys are
strictly less than |
abstract
Set<K>
|
keySet()
Returns a |
abstract
K
|
lastKey()
Returns the last (highest) key currently in this map. |
default
V
|
putFirst(K k, V v)
Throws |
default
V
|
putLast(K k, V v)
Throws |
default
SortedMap<K, V>
|
reversed()
Returns a reverse-ordered view of this map. |
abstract
SortedMap<K, V>
|
subMap(K fromKey, K toKey)
Returns a view of the portion of this map whose keys range from
|
abstract
SortedMap<K, V>
|
tailMap(K fromKey)
Returns a view of the portion of this map whose keys are
greater than or equal to |
abstract
Collection<V>
|
values()
Returns a |
Inherited methods | |
---|---|
Public methods
comparator
public abstract Comparator<? super K> comparator ()
Returns the comparator used to order the keys in this map, or
null
if this map uses the natural ordering of its keys.
Returns | |
---|---|
Comparator<? super K> |
the comparator used to order the keys in this map,
or null if this map uses the natural ordering
of its keys |
entrySet
public abstract Set<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 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.
Returns | |
---|---|
Set<Entry<K, V>> |
a set view of the mappings contained in this map, sorted in ascending key order |
firstKey
public abstract K firstKey ()
Returns the first (lowest) key currently in this map.
Returns | |
---|---|
K |
the first (lowest) key currently in this map |
Throws | |
---|---|
NoSuchElementException |
if this map is empty |
headMap
public abstract SortedMap<K, V> headMap (K 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.
Parameters | |
---|---|
toKey |
K : high endpoint (exclusive) of the keys in the returned map |
Returns | |
---|---|
SortedMap<K, V> |
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 does not permit null keys |
IllegalArgumentException |
if this map itself has a
restricted range, and toKey lies outside the
bounds of the range |
keySet
public abstract 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 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.
Returns | |
---|---|
Set<K> |
a set view of the keys contained in this map, sorted in ascending order |
lastKey
public abstract K lastKey ()
Returns the last (highest) key currently in this map.
Returns | |
---|---|
K |
the last (highest) key currently in this map |
Throws | |
---|---|
NoSuchElementException |
if this map is empty |
putFirst
public V putFirst (K k, V v)
Throws UnsupportedOperationException
. The encounter order induced by this
map's comparison method determines the position of mappings, so explicit positioning
is not supported.
Implementation Requirements:
- The implementation in this interface always throws
UnsupportedOperationException
.
Parameters | |
---|---|
k |
K : the key |
v |
V : the value |
Returns | |
---|---|
V |
the value previously associated with k, or null if none |
Throws | |
---|---|
UnsupportedOperationException |
always |
putLast
public V putLast (K k, V v)
Throws UnsupportedOperationException
. The encounter order induced by this
map's comparison method determines the position of mappings, so explicit positioning
is not supported.
Implementation Requirements:
- The implementation in this interface always throws
UnsupportedOperationException
.
Parameters | |
---|---|
k |
K : the key |
v |
V : the value |
Returns | |
---|---|
V |
the value previously associated with k, or null if none |
Throws | |
---|---|
UnsupportedOperationException |
always |
reversed
public SortedMap<K, V> reversed ()
Returns a reverse-ordered view of this map. The encounter order of mappings in the returned view is the inverse of the encounter order of mappings in this map. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the implementation permits modifications to this view, the modifications "write through" to the underlying map. Changes to the underlying map might or might not be visible in this reversed view, depending upon the implementation.
Implementation Requirements:
- The implementation in this interface returns a reverse-ordered SortedMap
view. The
reversed()
method of the view returns a reference to this SortedMap. Other operations on the view are implemented via calls to public methods on this SortedMap. The exact relationship between calls on the view and calls on this SortedMap is unspecified. However, order-sensitive operations generally delegate to the appropriate method with the opposite orientation. For example, callingfirstEntry
on the view results in a call tolastEntry
on this SortedMap.
Returns | |
---|---|
SortedMap<K, V> |
a reverse-ordered view of this map, as a SortedMap |
subMap
public abstract 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. (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.
Parameters | |
---|---|
fromKey |
K : low endpoint (inclusive) of the keys in the returned map |
toKey |
K : high endpoint (exclusive) of the keys in the returned map |
Returns | |
---|---|
SortedMap<K, V> |
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 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 |
tailMap
public abstract SortedMap<K, V> tailMap (K 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.
Parameters | |
---|---|
fromKey |
K : low endpoint (inclusive) of the keys in the returned map |
Returns | |
---|---|
SortedMap<K, V> |
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 does not permit null keys |
IllegalArgumentException |
if this map itself has a
restricted range, and fromKey lies outside the
bounds of the range |
values
public abstract 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 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.
Returns | |
---|---|
Collection<V> |
a collection view of the values contained in this map, sorted in ascending key order |