Map

1. What is a Map?

Map is an interface in the Collection Framework that stores data as key-value pairs. Every key is unique, and it's linked directly to one specific value, allowing quick lookup of a value using its key.

2. Why is it used?

Map is ideal when data naturally comes in pairs — like a student's roll number (key) linked to their name (value), letting you retrieve information quickly using just the key.

3. Real-Life Example

Think of a phonebook, where each contact name (key) is linked to a specific phone number (value). You look up a phone number directly by the name, without scanning through every entry.

4. Syntax

java
Map<KeyType, ValueType> mapName = new HashMap<>(); // or LinkedHashMap, TreeMap

5. Example Program

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

public class MapDemo {
    public static void main(String[] args) {
        Map<Integer, String> students = new HashMap<>();
        students.put(1, "Aman");
        students.put(2, "Neha");
        System.out.println(students.get(1));
    }
}

Output:

Aman

6. Key Points to Remember

• Map stores data as key-value pairs, and keys must be unique (values can repeat).
• Map does not extend the Collection interface, unlike List and Set.
• Common implementations include HashMap, LinkedHashMap, and TreeMap.