Gowtham Kalyan

Posted on Feb 20

Difference Between List, Set, and Map in Java

#java #list #map #set

The Java Collections Framework provides powerful data structures to store and manage data efficiently. Among them, List, Set, and Map are the most commonly used interfaces in real-world Java applications.

Understanding their differences is very important for students, freshers, and developers because this is one of the most frequently asked Java interview questions.

✅ What is List?

A List is an ordered collection that allows duplicate elements. Elements are stored based on index positions.

Example:

import java.util.ArrayList;
import java.util.List;

List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.add("Java"); // duplicates allowed

System.out.println(list);

Key Features:

Maintains insertion order
Allows duplicates
Supports index-based access
Example classes: ArrayList, LinkedList, Vector

✅ What is Set?

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

Example:

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

Set<String> set = new HashSet<>();
set.add("Java");
set.add("Python");
set.add("Java"); // duplicate ignored

System.out.println(set);

Key Features:

No duplicate values
Unordered (HashSet)
Faster search operations
Example classes: HashSet, LinkedHashSet, TreeSet

✅ What is Map?

A Map stores data in key-value pairs. Keys must be unique, but values can be duplicated.

Example:

import java.util.HashMap;
import java.util.Map;

Map<Integer, String> map = new HashMap<>();
map.put(1, "Java");
map.put(2, "Python");
map.put(1, "Spring"); // replaces previous value

System.out.println(map);

Key Features:

Stores key-value pairs
Keys are unique
Not part of Collection interface
Example classes: HashMap, LinkedHashMap, TreeMap, Hashtable