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java.util
public interface: SortedMap [javadoc | source]

All Implemented Interfaces:
    Map

All Known Implementing Classes:
    CheckedSortedMap, TreeMap, UnmodifiableSortedMap, ConcurrentNavigableMap, SubMap, NavigableMap, SubMap, DescendingSubMap, SynchronizedSortedMap, ConcurrentSkipListMap, AscendingSubMap, NavigableSubMap

A Map that further provides a total ordering on its keys. The map is ordered according to the {@linkplain Comparable natural 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 {@code entrySet}, {@code keySet} and {@code 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 {@code Comparable} interface (or be accepted by the specified comparator). Furthermore, all such keys must be mutually comparable: {@code k1.compareTo(k2)} (or {@code comparator.compare(k1, k2)}) must not throw a {@code ClassCastException} for any keys {@code k1} and {@code k2} in the sorted map. Attempts to violate this restriction will cause the offending method or constructor invocation to throw a {@code 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 {@code Map} interface. (See the {@code Comparable} interface or {@code Comparator} interface for a precise definition of consistent with equals.) This is so because the {@code Map} interface is defined in terms of the {@code equals} operation, but a sorted map performs all key comparisons using its {@code compareTo} (or {@code 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 {@code 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:

  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 type {@code Comparator}, which creates an empty sorted map sorted according to the specified comparator.
  3. A constructor with a single argument of type {@code Map}, 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 type {@code 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 {@code lowEndpoint} to {@code successor(highEndpoint)}. For example, suppose that {@code m} is a map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings in {@code m} whose keys are between {@code low} and {@code high}, 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 in {@code m} whose keys are between {@code low} and {@code high}, exclusive:
  SortedMap<String, V> sub = m.subMap(low+"\0", high);

This interface is a member of the Java Collections Framework.

Method from java.util.SortedMap Summary:
comparator,   entrySet,   firstKey,   headMap,   keySet,   lastKey,   subMap,   tailMap,   values
Method from java.util.SortedMap Detail:
 public Comparator<? super K> comparator()
    Returns the comparator used to order the keys in this map, or
{@code null} if this map uses the {@linkplain Comparable
natural ordering} of its keys.
 public Set<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 {@code remove} operation, or through the
{@code 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 {@code Iterator.remove},
{@code Set.remove}, {@code removeAll}, {@code retainAll} and
{@code clear} operations.  It does not support the
{@code add} or {@code addAll} operations.
 public K firstKey()
    Returns the first (lowest) key currently in this map.
 public SortedMap<K, V> headMap(K toKey)
    Returns a view of the portion of this map whose keys are
strictly less than {@code 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 {@code IllegalArgumentException}
on an attempt to insert a key outside its range.
 public 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 {@code remove} operation), the results of
the iteration are undefined.  The set supports element removal,
which removes the corresponding mapping from the map, via the
{@code Iterator.remove}, {@code Set.remove},
{@code removeAll}, {@code retainAll}, and {@code clear}
operations.  It does not support the {@code add} or {@code addAll}
operations.
 public K lastKey()
    Returns the last (highest) key currently in this map.
 public SortedMap<K, V> subMap(K fromKey,
    K toKey)
    Returns a view of the portion of this map whose keys range from
{@code fromKey}, inclusive, to {@code toKey}, exclusive.  (If
{@code fromKey} and {@code 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 {@code IllegalArgumentException}
on an attempt to insert a key outside its range.
 public SortedMap<K, V> tailMap(K fromKey)
    Returns a view of the portion of this map whose keys are
greater than or equal to {@code 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 {@code IllegalArgumentException}
on an attempt to insert a key outside its range.
 public 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 {@code remove} operation),
the results of the iteration are undefined.  The collection
supports element removal, which removes the corresponding
mapping from the map, via the {@code Iterator.remove},
{@code Collection.remove}, {@code removeAll},
{@code retainAll} and {@code clear} operations.  It does not
support the {@code add} or {@code addAll} operations.