A
SortedMap is a
Map that maintains its entries in ascending order, sorted according to the
keys' natural ordering, or according to a
Comparator
provided at the time of the
SortedMap creation. Natural ordering and
Comparators are discussed in the
Object Ordering section. The
SortedMap interface provides
operations for normal
Map operations and for the following:
-
Range view — performs arbitrary range operations on the sorted map
-
Endpoints — returns the first or the last key in the sorted map
-
Comparator access — returns the Comparator, if any, used to sort the map
The following interface is the
Map analog of
SortedSet.
public interface SortedMap<K, V> extends Map<K, V>{
Comparator<? super K> comparator();
SortedMap<K, V> subMap(K fromKey, K toKey);
SortedMap<K, V> headMap(K toKey);
SortedMap<K, V> tailMap(K fromKey);
K firstKey();
K lastKey();
}
Map Operations
The operations
SortedMap inherits from
Map
behave identically on sorted maps and normal maps with two exceptions:
-
The
Iterator returned by the iterator operation
on any of the sorted map's Collection views traverse the
collections in order.
- The arrays returned by the
Collection views'
toArray operations contain the keys, values, or
entries in order.
Although it isn't guaranteed by the interface, the
toString
method of the
Collection views in all the
Java platform's
SortedMap implementations returns a
string containing all the elements of the view, in order.
Standard Constructors
By convention, all general-purpose
Map implementations provide a
standard conversion constructor that takes a
Map;
SortedMap implementations are no exception. In
TreeMap,
this constructor creates an instance that orders its entries according to their
keys' natural ordering. This was probably a mistake. It would have been better to
check dynamically to see whether the specified
Map instance was a
SortedMap and, if so, to sort the new map according to the same
criterion (comparator or natural ordering). Because
TreeMap took
the approach it did, it also provides a constructor that takes a
SortedMap and returns a new
TreeMap containing
the same mappings as the given
SortedMap, sorted according to
the same criterion. Note that it is the compile-time type of the argument,
not its runtime type, that determines whether the
SortedMap
constructor is invoked in preference to the ordinary
map constructor.
SortedMap implementations also provide, by convention, a
constructor that takes a Comparator and returns an empty
map sorted according to the specified Comparator. If
null is passed to this constructor, it returns a
Map that sorts its mappings according to their keys'
natural ordering.
Comparison to SortedSet
Because this interface is a precise
Map analog of
SortedSet, all the idioms and code examples in
The SortedSet Interface section apply to
SortedMap with only trivial modifications.
