What is Map Interface in a Java

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Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value. This Map permits null value

In Java, the Map interface is a part of the Java Collections Framework and is used to represent a collection of key-value pairs where each key must be unique. It is designed to model the mathematical abstraction of a finite set of key-value pairs, where a key maps to a value.

The Map interface provides methods for adding, removing, and querying elements based on their keys. Some commonly used implementations of the Map interface in Java include HashMap, TreeMap, and LinkedHashMap.

Here’s a brief overview of the key characteristics of the Map interface:

  1. Key-Value Pairs: Each element in a Map is a key-value pair, where the key is used to identify the associated value.
  2. Unique Keys: Keys in a Map must be unique. Each key can map to at most one value.
  3. No Duplicate Values Restriction: Values in a Map can be duplicated. Different keys, however, must map to different values.
  4. Associative: The Map interface is often referred to as an associative container, as it associates keys with values.
  5. Null Values: In most implementations, null values are allowed, but some implementations may have restrictions on using null keys.

Example usage of a Map:

java
import java.util.HashMap;
import java.util.Map;public class MapExample {
public static void main(String[] args) {
// Creating a HashMap
Map<String, Integer> studentGrades = new HashMap<>();

// Adding key-value pairs
studentGrades.put(“Alice”, 90);
studentGrades.put(“Bob”, 85);
studentGrades.put(“Charlie”, 95);

// Accessing values using keys
int aliceGrade = studentGrades.get(“Alice”);
System.out.println(“Alice’s Grade: “ + aliceGrade);

// Iterating over the map
for (Map.Entry<String, Integer> entry : studentGrades.entrySet()) {
System.out.println(entry.getKey() + “: “ + entry.getValue());
}
}
}

In this example, studentGrades is a Map that associates student names (keys) with their corresponding grades (values). The HashMap class is used as the implementation of the Map interface.