# Set (Condensed Guide)

## What Is a Set?

A `Set` is a collection that **does not allow duplicate elements**.

Key characteristics:
- Stores **unique elements only**
- Does **not support indexing**
- Ordering depends on the implementation

Common implementations:
- `HashSet`
- `LinkedHashSet`
- `TreeSet`

```java
import java.util.Set;
import java.util.HashSet;

Set<Integer> numbers = new HashSet<>();

Iterable
 ↓
Collection
 ↓
Set

Implementations include:

Set
 ↓
HashSet
LinkedHashSet
TreeSet

A Set ensures every element is unique.

If you try to insert a duplicate element, it will not be added.

Example:

add(10)
add(20)
add(20)
add(30)

Result:

10, 20, 30

The duplicate 20 is ignored.

Actual performance depends on the implementation.

set.add(10);          // add element
set.remove(10);       // remove element
set.contains(10);     // check element
set.size();           // number of elements
set.isEmpty();        // check if empty

for (Integer num : set) {
    System.out.println(num);
}

Sets do not support get(index) because they are not indexed.

Use a Set when you need:

• Unique values
• Fast membership checks
• Removing duplicates from data

Examples:

• Unique usernames
• Tracking visited items
• Removing duplicate values from lists

Set is a collection that stores unique elements.

Key characteristics:

• No duplicate elements
• No indexing
• Different implementations provide different ordering behavior