SortedMap interface extends Map interface to further provide a total ordering on its keys.

Important Properties of SortedMap

• SortedMap is ordered according to the natural ordering of its keys, or by a Comparator typically provided at sorted map creation time.

• Order is reflected when iterating over the sorted map's collection views returned by the entrySet, keySet and values methods.

• SortedMap is the map analogue of SortedSet.

• All keys inserted into a sorted map must implement the Comparable interface or be accepted by the specified comparator.

• All keys must be mutually comparable or will cause the offending method or constructor invocation to throw a ClassCastException.

• The ordering maintained by a sorted map must be consistent with equals

  • 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 Map interface.

• All general-purpose sorted map implementation classes should provide four "standard" constructors:

  • A no argument constructor, which creates an empty sorted map.

  • 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.

• Such ranges submaps returned by various methods 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:

    • SortedMap<String, V> sub = m.subMap(low, high+"\0");

  • We can also generate an open range (which contains neither endpoint). 

    • SortedMap<String, V> sub = m.subMap(low+"\0", high);

Important Methods of SortedMap Interface

• comparator()

  • Returns the comparator used or null if this map uses the natural ordering of its keys.

• entrySet()

  • Returns a Set view of this map.

• firstKey()

  • Returns the first (lowest) key currently in this map.

• headMap(K toKey)

  • Returns a view portion of this map whose keys are strictly less than toKey.

• keySet()

  • Returns a Set view of the keys contained in this map.

• lastKey()

  • Returns the last (highest) key currently in this map.

• subMap(K fromKey, K toKey)

  • Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.

• tailMap(K fromKey)

  • Returns a view of the portion of this map whose keys are greater than or equal to fromKey.

• values()

  • Returns a Collection view of the values contained in this map.