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- Type Parameters:
K
- the type of keys maintained by this mapV
- the type of mapped values
- All Superinterfaces:
Map<K,V>
- All Known Subinterfaces:
ConcurrentNavigableMap<K,V>
,NavigableMap<K,V>
- All Known Implementing Classes:
ConcurrentSkipListMap
,TreeMap
public interface SortedMap<K,V> extends Map<K,V>
AMap
that further provides a total ordering on its keys. The map is ordered according to the natural ordering of its keys, or by aComparator
typically provided at sorted map creation time. This order is reflected when iterating over the sorted map's collection views (returned by theentrySet
,keySet
andvalues
methods). Several additional operations are provided to take advantage of the ordering. (This interface is the map analogue ofSortedSet
.)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)
(orcomparator.compare(k1, k2)
) must not throw aClassCastException
for any keysk1
andk2
in the sorted map. Attempts to violate this restriction will cause the offending method or constructor invocation to throw aClassCastException
.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 theComparable
interface orComparator
interface for a precise definition of consistent with equals.) This is so because theMap
interface is defined in terms of theequals
operation, but a sorted map performs all key comparisons using itscompareTo
(orcompare
) 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 theMap
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
tosuccessor(highEndpoint)
. For example, suppose thatm
is a map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings inm
whose keys are betweenlow
andhigh
, inclusive:SortedMap<String, V> sub = m.subMap(low, high+"\0");
A similar technique can be used to generate an open range (which contains neither endpoint). The following idiom obtains a view containing all of the key-value mappings inm
whose keys are betweenlow
andhigh
, exclusive:SortedMap<String, V> sub = m.subMap(low+"\0", high);
This interface is a member of the Java Collections Framework.
- Since:
- 1.2
- See Also:
Map
,TreeMap
,SortedSet
,Comparator
,Comparable
,Collection
,ClassCastException
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description Comparator<? super K>
comparator()
Returns the comparator used to order the keys in this map, ornull
if this map uses the natural ordering of its keys.Set<Map.Entry<K,V>>
entrySet()
Returns aSet
view of the mappings contained in this map.K
firstKey()
Returns the first (lowest) key currently in this map.SortedMap<K,V>
headMap(K toKey)
Returns a view of the portion of this map whose keys are strictly less thantoKey
.Set<K>
keySet()
Returns aSet
view of the keys contained in this map.K
lastKey()
Returns the last (highest) key currently in this map.SortedMap<K,V>
subMap(K fromKey, K toKey)
Returns a view of the portion of this map whose keys range fromfromKey
, inclusive, totoKey
, exclusive.SortedMap<K,V>
tailMap(K fromKey)
Returns a view of the portion of this map whose keys are greater than or equal tofromKey
.Collection<V>
values()
Returns aCollection
view of the values contained in this map.-
Methods declared in interface java.util.Map
clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, equals, forEach, get, getOrDefault, hashCode, isEmpty, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size
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Method Detail
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comparator
Comparator<? super K> comparator()
Returns the comparator used to order the keys in this map, ornull
if this map uses the natural ordering of its keys.- Returns:
- the comparator used to order the keys in this map,
or
null
if this map uses the natural ordering of its keys
-
subMap
SortedMap<K,V> subMap(K fromKey, K toKey)
Returns a view of the portion of this map whose keys range fromfromKey
, inclusive, totoKey
, exclusive. (IffromKey
andtoKey
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
- low endpoint (inclusive) of the keys in the returned maptoKey
- 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, totoKey
, exclusive - Throws:
ClassCastException
- iffromKey
andtoKey
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 iffromKey
ortoKey
cannot be compared to keys currently in the map.NullPointerException
- iffromKey
ortoKey
is null and this map does not permit null keysIllegalArgumentException
- iffromKey
is greater thantoKey
; or if this map itself has a restricted range, andfromKey
ortoKey
lies outside the bounds of the range
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headMap
SortedMap<K,V> headMap(K toKey)
Returns a view of the portion of this map whose keys are strictly less thantoKey
. 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
- 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
- iftoKey
is not compatible with this map's comparator (or, if the map has no comparator, iftoKey
does not implementComparable
). Implementations may, but are not required to, throw this exception iftoKey
cannot be compared to keys currently in the map.NullPointerException
- iftoKey
is null and this map does not permit null keysIllegalArgumentException
- if this map itself has a restricted range, andtoKey
lies outside the bounds of the range
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tailMap
SortedMap<K,V> tailMap(K fromKey)
Returns a view of the portion of this map whose keys are greater than or equal tofromKey
. 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
- 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
- iffromKey
is not compatible with this map's comparator (or, if the map has no comparator, iffromKey
does not implementComparable
). Implementations may, but are not required to, throw this exception iffromKey
cannot be compared to keys currently in the map.NullPointerException
- iffromKey
is null and this map does not permit null keysIllegalArgumentException
- if this map itself has a restricted range, andfromKey
lies outside the bounds of the range
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firstKey
K firstKey()
Returns the first (lowest) key currently in this map.- Returns:
- the first (lowest) key currently in this map
- Throws:
NoSuchElementException
- if this map is empty
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lastKey
K lastKey()
Returns the last (highest) key currently in this map.- Returns:
- the last (highest) key currently in this map
- Throws:
NoSuchElementException
- if this map is empty
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keySet
Set<K> keySet()
Returns aSet
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 ownremove
operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via theIterator.remove
,Set.remove
,removeAll
,retainAll
, andclear
operations. It does not support theadd
oraddAll
operations.
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values
Collection<V> values()
Returns aCollection
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 ownremove
operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via theIterator.remove
,Collection.remove
,removeAll
,retainAll
andclear
operations. It does not support theadd
oraddAll
operations.
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entrySet
Set<Map.Entry<K,V>> entrySet()
Returns aSet
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 ownremove
operation, or through thesetValue
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 theIterator.remove
,Set.remove
,removeAll
,retainAll
andclear
operations. It does not support theadd
oraddAll
operations.
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