Java TreeMap Class

Last Updated : 29 Mar 2026

Java TreeMap is used for storing key-value pairs in a sorted order which is useful when data needs to be accessed in a structured and ordered way. It is commonly used in applications where quick search, insertion, and deletion operations are required along with sorting.

In this chapter, you will learn about the Java TreeMap class, its working, features, and how it maintains sorted key-value pairs using a red-black tree.

What is Java TreeMap?

Java TreeMap is a class in the java.util package that implements the NavigableMap interface and extends the AbstractMap class. It is based on a red-black tree data structure and stores key-value pairs in sorted (ascending) order.

TreeMap allows only unique keys, does not permit null keys, but can contain multiple null values. It is non-synchronized and is mainly used when sorted data is required.

TreeMap Class Hierarchy

The TreeMap is part of the Collections Framework and follows a hierarchical structure where it extends the AbstractMap class and implements the NavigableMap interface. NavigableMap further extends SortedMap, which is a part of the Map interface. This hierarchy enables TreeMap to store elements in a sorted manner and provide navigation methods such as finding higher, lower, or nearest keys efficiently.

Key Points about TreeMap

The important points about Java TreeMap class are:

• The TreeMap stores data in the form of key-value pairs, where each key is associated with a specific value.
• It ensures that all keys are unique, which means duplicate keys are not allowed.
• It maintains elements in ascending order automatically using a red-black tree data structure.
• It provides efficient performance for operations such as search, insertion, and deletion.
• It does not allow null keys, but it supports multiple null values.
• It is non-synchronized, which makes it faster but not thread-safe by default.

TreeMap Class Declaration

Let's see the declaration for java.util.TreeMap class.

TreeMap Class Parameters

Let's see the Parameters for java.util.TreeMap class.

• K: It is the type of keys maintained by this map.
• V: It is the type of mapped values.

Constructors of TreeMap Class

Java TreeMap provides multiple constructors to create and initialize a TreeMap in different ways.

1. TreeMap()

This constructor constructs an empty TreeMap that is sorted according to the natural ordering of its keys.

Here is syntax:

2. TreeMap(Comparator comparator)

This constructor constructs an empty TreeMap that is sorted according to the specified comparator.

Here is syntax:

3. TreeMap(Map m)

This constructor constructs a TreeMap and initializes it with the entries from the specified map, sorted according to the natural ordering of the keys.

Here is syntax:

4. TreeMap(SortedMapm)

This constructor constructs a TreeMap and initializes it with the entries from the specified sorted map, maintaining the same ordering as the given map.

Here is syntax:

5. TreeMap(Collection c)

This constructor constructs a TreeMap containing the elements of the specified collection, sorted according to their natural ordering.

Here is syntax:

6. TreeMap(SortedMapm, Comparator comparator)

Constructs a TreeMap with the entries from the specified sorted map and sorts them using the provided comparator.

Here is syntax:

Methods of TreeMap Class

The TreeMap provides a variety of methods to perform operations such as insertion, deletion, searching, and navigation of elements in a sorted key-value structure.

The following table lists the commonly used methods of the TreeMap class along with their descriptions:

Examples of Java TreeMap Class

The following examples demonstrate how to use Java TreeMap for storing, removing, and navigating key-value pairs.

Example 1: Storing and Iterating TreeMap Elements

This example demonstrates how to store key-value pairs in a TreeMap and iterate through them.

Output:

100 Amit
101 Vijay
102 Ravi
103 Rahul

Example 2: Removing Elements from TreeMap

This example demonstrates how to remove an element using the remove() method.

Output:

Before invoking remove() method
100 Amit
101 Vijay
102 Ravi
103 Rahul
After invoking remove() method
100 Amit
101 Vijay
103 Rahul

Example 3: Using NavigableMap Methods

This example demonstrates various navigation methods such as descendingMap(), headMap(), tailMap(), and subMap().

Output:

descendingMap: {103=Rahul, 102=Ravi, 101=Vijay, 100=Amit}
headMap: {100=Amit, 101=Vijay, 102=Ravi}
tailMap: {102=Ravi, 103=Rahul}
subMap: {101=Vijay, 102=Ravi}

Example 4: Using SortedMap Methods

This example demonstrates how to use SortedMap methods like headMap(), tailMap(), and subMap().

Output:

headMap: {100=Amit, 101=Vijay}
tailMap: {102=Ravi, 103=Rahul}
subMap: {100=Amit, 101=Vijay}

Difference Between HashMap and TreeMap

The following table highlights the key differences between HashMap and TreeMap:

Complete Example: Storing Custom Objects (Book) in TreeMap

This example demonstrates how to store and retrieve objects of a custom class using a TreeMap.

Output:

1 Details:
101 Let us C Yashwant Kanetkar BPB 8
2 Details:
102 Data Communications & Networking Forouzan Mc Graw Hill 4
3 Details:
103 Operating System Galvin Wiley 6

Explanation

This example shows how a TreeMap can be used to store custom objects as values while maintaining the keys in sorted order. It also demonstrates how to traverse the map and access both keys and their corresponding object values.