feat(HashMapDemo4): add HashMap initialization with Map.of and dynamic updates

What
- Implemented `HashMapDemo4` to demonstrate creating a `HashMap` from an immutable `Map.of()`
  and then adding more entries dynamically.
- Prints the final map contents to show that new insertions work alongside the initial values.

Why
- `Map.of()` (Java 9+) creates a compact, immutable map which cannot be modified directly.
- Passing it into the `HashMap` constructor allows creating a **mutable copy** that can be updated.
- This demonstrates a modern and concise way to bootstrap a `HashMap` with initial values.

How
1. Created a `HashMap<Integer, String>` using `new HashMap<>(Map.of(...))` with entries `{0=A, 1=B, 2=C, 3=D}`.
2. Inserted additional entries dynamically using `put`:
   - `4 -> E`
   - `5 -> F`
   - `6 -> G`
3. Printed the map contents, which now includes both initial and newly added values.

Key Notes
- `Map.of(...)` creates an **immutable map**, so you cannot add/remove directly on it.
- Wrapping it with `new HashMap<>(...)` gives you a **mutable copy** that can be extended.
- `HashMap` does **not guarantee order** in output — order may vary depending on hashing.
- For predictable ordering: use `LinkedHashMap` (insertion order) or `TreeMap` (sorted order).

Real-world usage
- Useful for quickly initializing maps with default values/configuration,
  then extending them dynamically at runtime.

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

Author: Someshdiwan

Section25CollectionFramework/src/SortedMapDemo/TreeMapDemo/HashMapDemo.java renamed to Section 25 Collections Frameworks/Map Interface/HashMap/src/HashMapDemo4.java

@@ -1,11 +1,8 @@
-package SortedMapDemo.TreeMapDemo;
-
 import java.util.Map;
 import java.util.HashMap;
 
-public class HashMapDemo {
-    public static void main(String[] args)
-    {
+public class HashMapDemo4 {
+    public static void main(String[] args) {
         HashMap<Integer, String> HM = new HashMap<>(Map.of(0,"A",1,"B",2,"C",3,"D"));
 
         HM.put(4, "E");
@@ -14,4 +11,4 @@ public static void main(String[] args)
 
         System.out.println(HM);
     }
-}
+}