Set in Java – Simple Explanation

In Java, a Set is part of the Java Collections Framework and is used to store unique elements.

The main rule of Set:

No duplicate values allowed

What is a Set?

A Set is a collection that:

• Does not allow duplicates
• Does not maintain index
• Can store null values (depends on implementation)

Types of Set in Java

1. HashSet

• Does not maintain order
• Fast performance
• Allows one null value

HashSet<String> set = new HashSet<>();
set.add("Apple");
set.add("Banana");
set.add("Apple"); // duplicate ignored

System.out.println(set);

2. LinkedHashSet

• Maintains insertion order
• Slightly slower than HashSet

LinkedHashSet<String> set = new LinkedHashSet<>();
set.add("Apple");
set.add("Banana");
set.add("Mango");

System.out.println(set);

3. TreeSet

• Stores elements in sorted order
• Uses natural sorting
• Does not allow null

TreeSet set = new TreeSet<>();

set.add(30);
set.add(10);
set.add(20);

System.out.println(set); // [10, 20, 30]

Key Features of Set

• No duplicates
• Unordered (except LinkedHashSet & TreeSet)
• No index-based access
• Faster search operations

When to Use Set?

Use Set when:

• You want to remove duplicates
• You only care about unique values
• Order is not important (use HashSet)

List vs Set (Quick Idea)

Feature	List	Set
Duplicates	Allowed	Not allowed
Order	Maintained	Not guaranteed
Index access	Yes	No

Real-Life Example

Set → Like a collection of unique IDs
(No two IDs can be the same)

Final Thoughts

If your data should be unique, always go for Set instead of List.