TreeMap in Java Collections

The TreeMap class guarantees that the keys in the Map will be sorted in ascending order by either the keys natural order or by a Comparator provided to the constructor of the TreeMap. TreeMap implements Map and SortedSet interfaces and extends AbstractMap. TreeMap keeps the balanced binary tree in sorted order by key.

Searching for an item in a TreeMap will be slower than in a HashMap because the hashing algorithm gives better performance than the compareTo() method which is used to locate items in a TreeMap.

 

Creating a TreeMap – Constructors for TreeMap

It has the following constructors. Here comp stands for Comparator, mp stands for Map, smp stands for SortedMap.

Result	Constructor	Description
tmap =	new TreeMap()	Creates new TreeMap. Keys sorted by natural order.
tmap =	new TreeMap(comp)	Creates new TreeMap using Comparator comp to sort keys.
tmap =	new TreeMap(mp)	Creates new TreeMap from Map mp using natural ordering.
tmap =	new TreeMap(smp)	Creates new TreeMap from SortedMap smp using key ordering from smp.

 

Methods in TreeMap

TreeMap adds the methods from Map and SortedMap. See the methods of these interfaces – Methods in Map interface, Methods in SortedMap interface.

So other than Map interface methods it has SortedMap interface Methods:

• Object firstKey() - Gets the first key from the sorted Map.
• Object lastKey() - Gets the last key from the sorted map.
• SortedMap headMap(Object toKey) - Returns a view of the portion of this Map whose keys are less than toKey.
• SortedMap tailMap(Object fromKey) - Returns a view of the portion of this Map whose keys are greater than or equal to fromKey.
• SortedMap subMap(Object fromKey, Object toKey) - Returns a view of the portion of this Map whose starting key is greater than or equal to fromKey and whose ending key is less than toKey.

 

Example

TreeMap Example in java