What is the uniqueness of the LinkedHashSet data structure and how does it work?

LinkedHashSet is a data structure in Java that combines the properties of HashSet and LinkedHashMap.

Uniqueness and features:

• Stores unique elements (like HashSet).
• Preserves the insertion order of elements thanks to an internal linked list (Linked).

How it works:

• It is based on LinkedHashMap, where the set elements act as keys.
• When an element is added, it is placed in the hash table for quick lookup and simultaneously added to the linked list that maintains insertion order.
• During iteration, elements are returned in the order they were added.

Thus, LinkedHashSet provides:

• Fast access and existence check of elements (average O(1)).
• Iteration over elements in insertion order.

Example usage:

import java.util.LinkedHashSet;

public class Example {
    public static void main(String[] args) {
        LinkedHashSet<String> set = new LinkedHashSet<>();
        set.add("apple");
        set.add("banana");
        set.add("cherry");

        for (String fruit : set) {
            System.out.println(fruit);
        }
    }
}

Output will be:

apple
banana
cherry

This distinguishes LinkedHashSet from a regular HashSet, which does not guarantee element order.