TreeMap in java

TreeMap in java

The TreeMap class is sorted according to the natural order means ascending order of its keys, or you can provide by implementing a Comparator interface  provided at map creation time, depending on which constructor is used.

Java TreeMap is a part of collection since jdk 1.2 versions and available in java.util package. TreeMap implements the Map interface and extends AbstractMap class. TreeMap stores data in key & value pairs.

TreeMap - Here k means Key which is any data type

 V means Value of any data types

TreeMap in java - techfloaters

A Red-Black tree based on the NavigableMap interface implementation, This provides guaranteed log(n) time cost for the containsKey, get, put and remove operations.

TreeMap class Declaration

public class TreeMap

    extends AbstractMap

    implements NavigableMap, Cloneable, java.io.Serializable

Features of TreeMap class

1] TreeMap stores unique key only. Duplicate key not allowed if we try to enter then recent one get override by previous one.

2] TreeMap does not allow null key and if we try to add null key then at runtime throws  java.lang.NullPointerException Exaception.

3] TreeMap does not maintain insertion order because element are sorted based on the ascending order. So if you are using any class as key, make sure it’s implementing Comparable interface for natural ordering.

4] TreeMap allows multiple null values but key should not be null.

TreeMap class implementation is not synchronized.  

        If multiple threads access a map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally.

SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

5] The iterators returned by the iterator method of the collections returned by all of this class's "collection view methods" are fail-fast. If the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw exception named a ConcurrentModificationException. 

Constructor and Description

TreeMap<K, V> tm = new TreeMap()

Constructs a new, empty tree map, using the natural ordering of its keys.

TreeMap<K, V> tm = new TreeMap(Comparator comparator)

Constructs a new, empty tree map, ordered according to the given comparator.

TreeMap<K, V> tm = new TreeMap(Map m)

Constructs a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys.

TreeMap<K, V> tm = new TreeMap(SortedMap m)

Constructs a new tree map containing the same mappings and using the same ordering as the specified sorted map.

Java TreeMap Example

package com.vr.techfloaters;

import java.util.Iterator;

import java.util.Set;

import java.util.TreeMap;

import java.util.Map.Entry;

public class TreeMapDemo {

     public static void main(String[] args) {

          

           TreeMap tm = new TreeMap<>();

          

           //Adding elements

           tm.put(50, "java");

           tm.put(30, ".Net");

           tm.put(20, "php");

           tm.put(15, null);

           tm.put(35, "python");

           tm.put(10, null);

          

           //Get values based on key

           System.out.println(tm.get(20));

          

           //Remove key and values based on key

           System.out.println(tm.remove(10));

          

           //Iterating the element in HashMap

           Set< Entry > set = tm.entrySet();

           Iterator> itr = set.iterator();

           while(itr.hasNext()){

                 Entry entry = itr.next();

                 System.out.println(entry.getKey() +" : "+entry.getValue());

           }

     }

   

}

Output

php

null

15 : null

20 : php

30 : .Net

35 : python

50 : java

That’s all for a basic concept for TreeMap in java, I hope that you enjoyed reading it and let us know in comment if anything you want.