Collection - The SortedMap InterfaceA 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. TheSortedMap interface provides operations for normal Map operations and for the following:
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:
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 SortedMapconstructor 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. |