🎯 1. What is the Set Interface?

Set is a collection that does NOT allow duplicate elements.

Key guarantees:

✔ No duplicates

✔ No index-based access

✔ Order depends on implementation

If you add the same element twice → it’s stored once.

⭐ 2. Why Set Exists?

Because many real-world problems need uniqueness:

✔ Unique usernames

✔ Unique email IDs

✔ Unique tags

✔ Remove duplicates from a list

Set handles this automatically.

🧱 3. Set Interface Hierarchy

Collection
   └── Set
        ├── HashSet
        ├── LinkedHashSet
        └── TreeSet