TreeSet in Java

A TreeSet in Java is a collection that implements the NavigableSet interface and uses a TreeMap internally to store elements.

Key Properties of TreeSet

TreeSet provides an ordered set implementation that sorts elements based on their natural ordering or according to a specified comparator.

When you need to maintain a collection of unique elements in a sorted order, you can go for TreeSet.

Example Suppose you are developing an application for managing a library. You need to keep track of the titles of the books in sorted order to facilitate searching and displaying the books in alphabetical order.

public class LibraryManager {  
    public static void main(String[] args) {  
        TreeSet<String> bookTitles = new TreeSet<>();  
        bookTitles.add("To Kill a Mockingbird");  
        bookTitles.add("1984");  
        bookTitles.add("Pride and Prejudice");  
        bookTitles.add("Queen of England");  
        bookTitles.add("The Catcher in the Rye");  
        bookTitles.add("1984"); // Duplicate title, will not be added again  

        // Display the book titles in sorted order
        System.out.println("Book titles (sorted):");
        for (String title : bookTitles) {  
            System.out.println(title);  
        }  

        // Finding the first and last book titles  
        System.out.println("\nFirst book in the library: " + bookTitles.first());  
        System.out.println("Last book in the library: " + bookTitles.last());  

        // Displaying a subset of books  
        System.out.println("\nBooks between 'P' and 'T':");  
        for (String title : bookTitles.subSet("P", "T")) {  
            System.out.println(title);  
        }  
    }  
}

Output:

Book titles in the library (sorted):
1984
Pride and Prejudice
Queen of England
The Catcher in the Rye
To Kill a Mockingbird

First book in the library: 1984
Last book in the library: To Kill a Mockingbird

Books between 'P' and 'T':
Pride and Prejudice
Queen of England