TreeMap in Java with Example

TreeMap in Java is a class which extends AbstractMap and implements the NavigableMap interface. It creates a map that is stored in a tree structure. The TreeMap provides an efficient way of storing key/values pair in sorted order and allows fast retrieval. A TreeMap guarantees that its elements will be stored in ascending key order. Some of the important points of the TreeMap are:

1. TreeMap doesn't have null keys but it may have multiple null values.
2. It contains only unique elements.
3. TreeMap guarantees that its elements will be stored in ascending key order.
4. Java TreeMap is not synchronized.

Constructors in Java TreeMap:

The following TreeMap constructors are defined:

1. TreeMap(): This constructor creates an empty tree map that will be sorted according to natural sorting order.

2. TreeMap(Comparator comparator): It creates an empty tree map that will be sorted by using the Comparator.

3. TreeMap(Map m): It initializes the tree map with the entries from m.

4. TreeMap(SortedMap sm): It initializes the tree map with the entries from sm.

Methos of Java TreeMap:

1. Object put(Object key, Object value): This method is used to put key and values into a map.

2. void putAll(Map map): This method is used to copies all of the elements from the specified map to this map.

3. Object firstKey(): This method returns the first key from the sorted map.

4. Object lastKey(): This method returns the last key from the sorted map.

5. Object get(Object key): returns the value associated with the specified key.

6. int size(): returns the number of key/values pair in this map.

7. void clear(): removes all the entries from this map.

8. Object clone(): returns a shallow copy of a tree map.

9. boolean containsKey(Object key): returns true if this map contains the specified key.

9. boolean containsValue(Object value): returns true if this map contains the specified value.

10. Collection values(): This method returns a collection containing the values in the map.

11. Set keySet(): returns a set of keys in the invoking map.

12. Set entrySet(): returns a set of entries in the invoking map.

13. SortedMap headMap(key end): This method returns a sorted map for those map entries with keys that are less than the end.

14. SortedMap tailMap(key start): This method returns a sorted map for those map entries with keys that are greater than or equal to start.

15. SortedMap subMap(key start, key end): This method returns a sorted map for those map entries with keys that are greater than or equal to start and less than the end.

Reference: TreeMap official Documentation

TreeMap Example


import java.util.*;
class TreeMapExample{
 public static void main(String args[]){
  
  //creating a tree map
  TreeMap<Integer, String> tmap = new TreeMap<Integer, String>();
  
  //adding values in this map
  tmap.put(101, "Rahul");
  tmap.put(109, "Amit");
  tmap.put(103, "Vijay");
  tmap.put(102, "Suresh");
  tmap.put(108, "Prashant");
  
  //returns size of tree map
  System.out.println("Tree map size is: "+tmap.size());
  
  //check tree map contains specified key or not
  System.out.println("Specified key present or not: "+tmap.containsKey(103));
  
  ////check tree map contains specified value or not
  System.out.println("Specified value present or not: "+tmap.containsValue("Prashant"));
  
  //returns tree map first key
  System.out.println("Tree Map first key is: "+tmap.firstKey());
  
  //return tree map last key
  System.out.println("Treemap last key is: "+tmap.lastKey());
  
  //returns value with specified key
  System.out.println("Retrieve value associated with specified key: "+tmap.get(108));
  
  //return key set
  System.out.println("Key set is: "+tmap.keySet());
  
  //return entry set
  System.out.println("Entry Set is: "+tmap.entrySet());
  
  //removes all the mapping
  tmap.clear();
  System.out.println("Removes all mapping from tree map: " +tmap);
 }
}

Output:

HashMap vs TreeMap in Java

HashMap and TreeMap both are used to key/value pairs in their object but there are some differences between HashMap and TreeMap which is very important for you to know which is shown below: