**What Data Structure Is Used in TreeMap?**

A __TreeMap__ is a type of **data structure** that is commonly used in computer science and programming. It is an implementation of the ** SortedMap** interface in Java, which means that it stores key-value pairs in a sorted order based on the keys.

## Overview of TreeMap

The __TreeMap__ class in Java is part of the * Java Collections Framework*. It provides an efficient way to store, retrieve, and manipulate data by using a self-balancing binary search tree. This allows for fast operations such as inserting, deleting, and searching elements.

The underlying data structure used by __TreeMap__ is a * Red-Black Tree*. This is a type of binary search tree that has additional properties to ensure its balance. The Red-Black Tree guarantees that the height of the tree remains logarithmic, which results in efficient operations with a worst-case time complexity of O(log n).

## Main Features of TreeMap

The TreeMap class provides several features that make it a popular choice for storing and retrieving data:

__Sorted Order:__The elements stored in a TreeMap are automatically sorted according to their keys. This allows for efficient searching and range-based operations.__Duplicates:__TreeMap does not allow duplicate keys. If you attempt to insert an element with an existing key, it will replace the existing value with the new one.__Navigable Operations:__TreeMap provides methods for navigating through the map such as finding the first or last key, or retrieving a submap based on a range of keys.__Efficient Operations:__Due to the self-balancing nature of the Red-Black Tree, operations like insertion, deletion, and searching have a worst-case time complexity of O(log n).

## Usage of TreeMap

The TreeMap class is commonly used in scenarios where data needs to be stored in a sorted order and efficient retrieval is required. Some use cases include:

__Dictionary:__TreeMap can be used to implement a dictionary where words are stored as keys and their meanings as values. The sorted nature of the TreeMap makes it easy to search for words and retrieve their meanings efficiently.__Event Scheduling:__TreeMap can be used to schedule events based on their start time.The TreeMap will automatically sort the events by their start time, allowing for efficient retrieval of upcoming events.

__Range-based Operations:__With methods like subMap and headMap, TreeMap makes it easy to perform operations on a subset of elements based on their keys. This can be useful in applications that require range-based queries.

### Conclusion

In summary, TreeMap is a powerful data structure in Java that provides efficient storage and retrieval of key-value pairs in sorted order. Its underlying Red-Black Tree ensures balance and logarithmic height, resulting in fast operations with a worst-case time complexity of O(log n). With its features such as sorted order, navigable operations, and efficient performance, TreeMap is widely used in various applications where sorted data is required.

*Note: When using the TreeMap class in Java, it is important to ensure that the keys implement the Comparable interface or provide a Comparator to define the sorting order.*