Java TreeSet Class

TreeSet belongs to the Java Collections Framework and serves as an implementation of the NavigableSet interface. A TreeMap forms the foundation for TreeSet which stores elements in sorted ascending order. TreeSet elements are stored in natural order or according to a custom comparator unlike an unordered HashSet.

Key Features

• A sorted set arranges elements in their natural sequence such as numbers which are arranged from the smallest to the largest value.
• No duplicates allowed
• No null elements (throws NullPointerException)
• Implements NavigableSet, SortedSet, and Set
• Backed by a Red-Black Tree

Syntax

TreeSet set = new TreeSet<>(); 

Example

TreeSet numbers = new TreeSet<>();
 

Example

import java.util.TreeSet;

public class TreeSetExample {
    public static void main(String[] args) {
        TreeSet names = new TreeSet<>();

        // Add elements
        names.add("Zara");
        names.add("Alex");
        names.add("John");
        names.add("Emma");

        // Print sorted set
        System.out.println("Names: " + names); // [Alex, Emma, John, Zara]

        // Check and remove
        System.out.println("Contains John? " + names.contains("John"));
        names.remove("Zara");

        // Display final set
        for (String name : names) {
            System.out.println(name);
        }

        // Bounds
        System.out.println("First: " + names.first());
        System.out.println("Last: " + names.last());
    }
}

Note

• Inserting null values into this data structure causes a NullPointerException.
• The TreeSet performs slower than HashSet operations for adding, searching, and removing elements since it preserves a sorted sequence which requires O(log n) time complexity.
• This data structure suits situations where automatic element sorting and range queries are required

TreeSet vs HashSet vs LinkedHashSet