feat: Demonstrate combined use of instance and static (global) variables in BankAccount model [bank-static-instance]

🎯 Purpose:
Show how instance and static variables can coexist to model both per-object and shared data using a banking context.

📌 Key Features:
- 👤 **Instance Variables** (`accountHolder`, `balance`): Unique for each `BankAccount` object.
- 🌐 **Static Variable** (`interestRate`): Shared across all bank accounts globally.
- 🔁 When `interestRate` is updated (e.g., from 5.0% to 6.5%), **all accounts reflect the change** automatically.
- 💰 Method `calculateInterest()` computes interest dynamically using the shared rate.

📦 Class Breakdown:
- `BankAccount`: Contains logic for interest calculation and displaying account details.
- `CombinedUseOfInstanceGlobalVariable`: Main runner that creates multiple accounts, displays data, and shows the effect of modifying the static variable.

📊 Use Case Summary:

| Type                   | Example Use in Code                              |
|------------------------|--------------------------------------------------|
| Instance Variables     | `accountHolder`, `balance`                       |
| Global Static Variable | `interestRate` shared by all accounts            |
| Combined Usage         | Changing global rate updates all account output  |

🔑 Key: `bank-static-instance`

✅ Reinforces the power of `static` for shared constants/configs and instance fields for per-object state.

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

Author: Someshdiwan

Section10Methods/LocalandGlobalVariables/src/CombinedUseOfInstanceGlobalVariable.java

@@ -1,10 +1,3 @@
-/* 
-Key Features:
-Each account has its own accountHolder and balance (Instance Variables).
-interestRate is shared across all accounts (Global Variable).
-Updating interestRate affects all accounts.
-*/
-
 class BankAccount {
     private String accountHolder;  // Instance variable (unique per object)
     private double balance;        // Instance variable