feat(HashMapDemo2): add simple HashMap insertion and print demo

What
- Implemented a minimal `HashMapDemo2` that shows how to add entries into a `HashMap` and print its contents.

Why
- To demonstrate the basic usage of `HashMap` for storing key–value pairs.
- Provides a quick example of how insertion works and how the default `toString()` shows map contents.

How
1. Created a `HashMap<Integer, String>` called `HM`.
2. Inserted five entries using `put(key, value)`.
3. Printed the map directly with `System.out.println(HM)`.

Logic
- Keys: `1 → 5` (integers).
- Values: `"Hello"`, `"World"`, `"This is the Hash Map"`, `"Adding elements"`, `"Done"`.
- `HashMap` internally uses hashing to determine bucket placement.
- Printing shows all entries in `{key=value, ...}` format, but order is **not guaranteed** (depends on hash distribution).

Real-life applications
- Basic key–value storage: e.g., mapping user IDs to user names, student roll numbers to details, or product IDs to descriptions.
- Fast lookups (average O(1) time complexity).

Notes
- `HashMap` allows **null keys** (only one) and **multiple null values**.
- Not synchronized — use `ConcurrentHashMap` in multithreaded environments.
- If insertion order is important, use `LinkedHashMap`.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section25CollectionFramework/src/HashMapDemo/HashMapDemo2.java renamed to Section 25 Collections Frameworks/Map Interface/HashMap/src/HashMapDemo2.java

@@ -1,4 +1,3 @@
-package HashMapDemo;
 import java.util.HashMap;
 
 public class HashMapDemo2 {
@@ -10,6 +9,7 @@ public static void main(String[] args) {
         HM.put(3, "This is the Hash Map");
         HM.put(4, "Adding elements");
         HM.put(5, "Done");
+
         System.out.println(HM);
     }
-}
+}