Map in Java

Source: Dev.to

What is Map in Java Collections?

A Map in Java (from the Java Collections Framework) is a data structure that stores data in key–value pairs.

• Each key is unique.
• Each value is associated with a key.

Think of it like a dictionary: word → meaning.

Example

101 → "John"
102 → "Alice"

Why do we use Map?

We use a Map when:

• We need fast lookup using a key.
• We want to store pairs of related data.
• We need unique keys.

Real‑world examples

• Student ID → Name
• Username → Password
• Product ID → Price

Common Map Implementations

• HashMap – Fast, unordered.
• LinkedHashMap – Maintains insertion order.
• TreeMap – Sorted by keys.

Important Methods

• put(key, value) – Insert data.
• get(key) – Retrieve the value for a key.
• remove(key) – Delete the entry for a key.
• containsKey(key) – Check if a key exists.
• keySet() – Get a set of all keys.

Difference between Map vs List vs Set?