Module java.base
Package java.util

Interface SortedMap<K,V>

Type Parameters:
K - the type of keys maintained by this map
V - 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 interfaceSortedMap<K,V>extendsMap<K,V>
AMap that further provides atotal ordering on its keys. The map is ordered according to thenatural 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 theComparable interface (or be accepted by the specified comparator). Furthermore, all such keys must bemutually 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 beconsistent with equals if the sorted map is to correctly implement theMap interface. (See theComparable interface orComparator interface for a precise definition ofconsistent 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 mapis 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:

  1. A void (no arguments) constructor, which creates an empty sorted map sorted according to the natural ordering of its keys.
  2. A constructor with a single argument of typeComparator, which creates an empty sorted map sorted according to the specified comparator.
  3. A constructor with a single argument of typeMap, which creates a new map with the same key-value mappings as its argument, sorted according to the keys' natural ordering.
  4. A constructor with a single argument of typeSortedMap, 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 arehalf-open, that is, they include their low endpoint but not their high endpoint (where applicable). If you need aclosed range (which includes both endpoints), and the key type allows for calculation of the successor of a given key, merely request the subrange fromlowEndpoint 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 anopen 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:

  • Method Details

    • comparator

      Comparator<? superK> comparator()
      Returns the comparator used to order the keys in this map, ornull if this map uses thenatural ordering of its keys.
      Returns:
      the comparator used to order the keys in this map, ornull 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 anIllegalArgumentException on an attempt to insert a key outside its range.

      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 fromfromKey, 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 keys
      IllegalArgumentException - iffromKey is greater thantoKey; or if this map itself has a restricted range, andfromKey ortoKey lies outside the bounds of the range

    • 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 anIllegalArgumentException 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 thantoKey
      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 keys
      IllegalArgumentException - if this map itself has a restricted range, andtoKey lies outside the bounds of the range

    • 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 anIllegalArgumentException 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 tofromKey
      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 keys
      IllegalArgumentException - if this map itself has a restricted range, andfromKey lies outside the bounds of the range

    • 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

    • 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

    • 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.
      Specified by:
      keySet in interface Map<K,V>
      Returns:
      a set view of the keys contained in this map, sorted in ascending order

    • 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.
      Specified by:
      values in interface Map<K,V>
      Returns:
      a collection view of the values contained in this map, sorted in ascending key order

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