docs: Add practical applications and examples of global (static) variables in Java [global-static-use cases]

🔑 Key: global-static-use cases
🧠 Highlights:
- Shared Configuration: Use static variables for database URLs, API keys, or application-wide settings.
- Object Tracking: Track number of created instances using a static counter (`userCount`).
- Shared Resources: Manage memory, resource pools, or connection instances across the app.
- Constants: Define shared values like tax rates or interest rates (`Bank.interestRate`).
- Logging Control: Toggle logging globally with static flags (`Logger.isDebugMode`).
- Game Dev Use: Keep global game limits or shared scoreboard values (`MAX_PLAYERS`, `highestScore`).
- Singleton Pattern: Maintain a single instance via static reference and controlled access (`DatabaseConnection.getInstance()`).

📚 Purpose:
- Demonstrates how `static` variables support data sharing, optimization, and consistency across instances.
- Useful in scenarios where a value or instance must be consistent throughout the application.

✅ Covers both real-world applications and design pattern usage (e.g., Singleton).

Signed-off-by: Somesh diwan <[email protected]>

Author: Someshdiwan

Section10Methods/LocalandGlobalVariables/src/Applications Of Global Variable.txt

@@ -20,6 +20,7 @@ class User {
         userCount++;  // Increase count every time an object is created
     }
 }
+
 This helps in monitoring the total number of active users in a system.
 
 3. Managing Shared Resources
@@ -51,7 +52,7 @@ Global Scoreboard (static int highestScore;)
 Example: Singleton Design Pattern (Ensuring only one instance of a class is created).
 
 class DatabaseConnection {
-    private static DatabaseConnection instance;  // Global shared instance
+    private static DatabaseConnection instance; // Global shared instance
 
     private DatabaseConnection() {} // Private constructor to prevent multiple instances
 
@@ -62,4 +63,5 @@ class DatabaseConnection {
         return instance;
     }
 }
-Used in databases to prevent multiple connections from being created.
+
+Used in databases to prevent multiple connections from being created.