TreeMap in java with examples

TreeMap class implements Map similar to HashMap.

Some important points about TreeMap:

  1. TreeMap implements Map interface and extends HashMap class.
  2. TreeMap is implemented using Red black tree based NavigableMap.
  3. TreeMap is ordered collection and store its elements in natural ordering of keys.
  4. Key which you would like to put in TreeMap must implement Comaparable interface or you can use Comparator for custom sorting
When you run above program, you will get following output:
As you can see, it is sorted in ascending order of Key(Country)

What if you want custom sorting rather than natural ordering:

If you want custom sorting , then you can using below TreeMap constructor. You can define your own comparator.

Example: Create as below
Create TreeMapCompMain as below:
When you run above program, you will get below output:

You can pass HashMap to constructor of TreeMap to sort it on Key

By passing HashMap to constructor of TreeMap, you can sort TreeMap.

Create as below. It should implement Comparable interface
Create as below:
When you run program, you will get below output:


You may also like:

Related Posts

  • 02 October

    Initialize ArrayList with values in Java

    In this article, we will learn to initialize ArrayList with values in Java. ArrayList is an implementation class of List interface in Java. It is used to store elements. It is based on a dynamic array concept that grows accordingly. We can Initialize ArrayList with values in several ways. Let’s see some of them with […]

  • 17 March

    PriorityQueue in Java 8

    In this post, we will see about Java 8 PriorityQueue. When the objects are supposed to be processed on the basis of their priority, in that scenario we use PriorityQueue. It’s a special type of queue (also, unbound queues) where the elements can be ordered either as per their natural ordering or based on a […]

  • 06 October

    2d Arraylist java example

    In this post, we will see how to create 2d Arraylist in java. Best way to create 2d Arraylist is to create list of list in java. [crayon-603c0d11aea66155890770/] Let’s create a program to implement 2d Arraylist java. [crayon-603c0d11aea6b208499689/] Output: 2nd element in list3 : List3_Str2 3nd element in list1 : List1_Str3 1st element in list2 […]

  • 04 May

    How HashMap works in java

    Most common interview questions are <code>How HashMap works in java</code>, “How get and put method of HashMap work internally”. Here I am trying to explain internal functionality with an easy example. [crayon-603c0d11ce9bb123028934-i/]  is one of the most used Collections in java.Rather than going through theory, we will start with example first, so that you will […]

  • 21 October

    How to Sort HashSet in Java

    In this post, we will see how to sort HashSet in java. HashSet is a collection which does not store elements in any order. You might come across a situation where you need to sort HashSet. There can be many ways to sort HashSet, we will see two methods here. Using TreeSet You can use […]

  • 20 October

    Java Array to Set

    In this post, we will learn java array to set conversion. There are many ways to convert array to set. 1. Using Java 8’s Stream If you are using Java 8, I would recommend using this method. [crayon-603c0d11cf5d7165854798/] Output [John, Martin, Mary] 2. Using HashSet constructor() We can directly call HashSet‘s constructor for java set […]

Leave a Reply

Your email address will not be published. Required fields are marked *

Subscribe to our newletter

Get quality tutorials to your inbox. Subscribe now.