Maps

Maps in Java represent a collection of key-value pairs where each key is unique. They allow efficient retrieval, insertion, and deletion of elements based on keys. The Java Collections Framework provides several implementations of the Map interface. Here's an explanation along with examples:

Explanation:

1. Key-Value Pairs:

   - Maps store data in key-value pairs.

   - Each key is associated with exactly one value, and keys are unique within a Map.

2. No Duplicate Keys:

   - Keys in a Map must be unique. Adding a duplicate key will replace the existing value.

3. Key-Based Operations:

   - Maps provide methods to manipulate elements based on keys, such as `put()`, `get()`, `remove()`, etc.

4. Common Implementations:

   - `HashMap`: Implements a hash table for storing key-value pairs.

   - `TreeMap`: Implements a sorted map using a Red-Black tree.

   - `LinkedHashMap`: Maintains insertion order.

Example Demonstrations:

Let's demonstrate using some common implementations of the Map interface:

1. HashMap Example:

import java.util.HashMap;

import java.util.Map;

public class HashMapExample {

    public static void main(String[] args) {

        // Creating a HashMap

        Map<String, Integer> map = new HashMap<>();

        // Adding key-value pairs to the map

        map.put("Apple", 10);

        map.put("Banana", 20);

        map.put("Orange", 15);

        map.put("Apple", 30); // Overwrites the previous value

        // Printing the map

        System.out.println("Map: " + map);

        // Removing a key-value pair

        map.remove("Banana");

        // Checking if a key is present

        System.out.println("Contains key 'Orange'? " + map.containsKey("Orange"));

        // Size of the map

        System.out.println("Size of map: " + map.size());

    }

}

2. TreeMap Example:

import java.util.Map;

import java.util.TreeMap;

public class TreeMapExample {

    public static void main(String[] args) {

        // Creating a TreeMap

        Map<String, Integer> map = new TreeMap<>();

        // Adding key-value pairs to the map

        map.put("Orange", 15);

        map.put("Apple", 10);

        map.put("Banana", 20);

        // Printing the map

        System.out.println("Map: " + map);

    }

}

3. LinkedHashMap Example:

import java.util.LinkedHashMap;

import java.util.Map;

public class LinkedHashMapExample {

    public static void main(String[] args) {

        // Creating a LinkedHashMap

        Map<String, Integer> map = new LinkedHashMap<>();

        // Adding key-value pairs to the map

        map.put("Orange", 15);

        map.put("Apple", 10);

        map.put("Banana", 20);

        // Printing the map

        System.out.println("Map: " + map);

    }

}

Output:

1. HashMap Example:

Map: {Orange=15, Apple=30}

Contains key 'Orange'? true

Size of map: 2

2. TreeMap Example:

Map: {Apple=10, Banana=20, Orange=15}

3. LinkedHashMap Example:

Map: {Orange=15, Apple=10, Banana=20}

These examples demonstrate the usage of HashMap, TreeMap, and LinkedHashMap, highlighting their unique characteristics and behavior. Depending on your requirements, you can choose the appropriate Map implementation.