TreeMap is a Java collection that structures the data in the form of an ordered key and their respective values. It has been available since JDK 1.2. Internally, TreeMap uses a red-black tree to structure the data, which is a self-balancing binary tree. The keys in TreeMap are unique identifiers, and by default, TreeMap arranges the data in a natural ordering of keys.
For the integer keys, it is stored in the ascending order of the keys, and for the String key, the data will be stored in the alphabetic order. We can always override the default ordering of data and can inject custom sorting by using a comparator during the TreeMap creation to sort in any defined manner as per the logic provided in the comparator. We will discuss in detail a few of the custom hybrid sorting approaches along with some code examples in this article.