docs: Add Account hierarchy explanation and interview/system-design notes

WHAT the update contains:
Provides a clear explanation of the Account class hierarchy (Account, SavingsAccount, LoanAccount) and the main demo (InheritanceIMP).
Describes the code-level concepts demonstrated:
- Encapsulation via private fields and getters/setters
- Inheritance through SavingsAccount and LoanAccount
- Method overriding and specialized behaviors (deposit, withdraw, payEMI, repay)
- Polymorphism use-cases and access considerations
Includes interview-ready talking points about design, trade-offs, and what to cover in system design interviews (OOP, SOLID, concurrency, patterns, DB design, caching, microservices).

WHY this matters:
Documents both the implementation intent and how to explain it in interviews, turning code into teachable material.
Helps reviewers and future you succinctly explain design decisions and trade-offs without re-deriving them from code.
Equips you to answer follow-up interview questions (why not performance improvement from encapsulation, why protected vs private balance, constructor choices, error handling strategy).

HOW it works:
Summarizes the code behavior:
- Account: base fields (accNo, name, address, phno, dob) with getters and minimal setters, protected balance.
- SavingsAccount: deposit and withdraw with validation, balance increases/decreases.
- LoanAccount: initialized with loan amount as balance; payEMI and repay reduce outstanding loan and avoid negative balances.
Explains runtime behavior shown in InheritanceIMP:
- Demonstrates deposits/withdrawals and loan repayments with prints for verification.
Provides interview answers and checklist to discuss when asked about system design (requirements, components, trade-offs, optimizations).

Tips and gotchas:
Do not claim encapsulation improves runtime performance; its benefits are maintainability, safety, and modularity.
balance is protected for convenience in subclasses but making it private and exposing protected helper methods is safer for encapsulation.
For production readiness, add input validation (throw exceptions on invalid operations), transactional guarantees for banking ops, and proper logging/auditing.
Consider using Account references to hold SavingsAccount or LoanAccount instances in demos to illustrate polymorphism.
When preparing for interviews, be ready to discuss scaling the design (sharding accounts, consistency models, caching strategies, idempotency, monitoring).

Use-cases:
Repository documentation for onboarding and interview prep.
In-repo teaching material for junior engineers to learn OOP, inheritance, and banking domain modelling.
Starter template for evolving into a more robust banking simulation or microservice (accounts service, ledger, transaction processing).

Short key: docs-account-hierarchy banking-demo interview-guide.

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

Author: Someshdiwan

Section12Inheritance/src/InheritanceIMP Code Logic Explanation for Interview.txt renamed to Section12Inheritance/src/Code Logic Explanation for Interview.txt

@@ -8,7 +8,6 @@ Your program demonstrates inheritance in Java, specifically:
 
 Enhanced performance is not a direct benefit of encapsulation in Java.
 While encapsulation improves code maintainability, provides better control over data access, and increases modularity,
-
 it doesn't necessarily enhance performance.
 
 Encapsulation is primarily about information hiding and creating a clear separation between the internal implementation
@@ -17,7 +16,6 @@ of a class and its public interface, which helps in managing complexity and impr
 ---
 
 1. Base Class: `Account`
-     
      - This is a superclass containing attributes for:
      - Account number (`accNo`)
      - Name (`name`)
@@ -30,27 +28,22 @@ of a class and its public interface, which helps in managing complexity and impr
      - Setter methods allow updating `address` and `phno`.
 
 2.  Subclass: `SavingsAccount` (Regular Bank Account):
-
    - Extends `Account`, meaning it inherits all properties of `Account`.
    - Implements deposit() and withdraw() methods.
    - Withdrawal is restricted (prevents overdrawing).
 
 3. Subclass: `LoanAccount` (Credit/Debt System):
-   
    - Also extends `Account`, but balance here represents debt.
    - Implements payEMI() and repay():
    - `payEMI()` reduces debt partially.
    - `repay()` allows paying off the entire loan.
    - Ensures debt does not go negative.
 
 4. Main Class (`InheritanceIMP`):
-   
    - Creates a `SavingsAccount` and `LoanAccount` object.
    - Tests `deposit()`, `withdraw()`, `payEMI()`, and `repay()`.
    - Prints results to verify the implementation.
 
----
-
 How to Explain System Design in Interviews:
 
 System design focuses on scalability, performance, and reliability. Interviewers expect you to:
@@ -59,8 +52,6 @@ System design focuses on scalability, performance, and reliability. Interviewers
 3. Consider trade-offs (scalability vs. consistency).
 4. Optimize for performance (caching, load balancing).
 
----
-
 Basic Concepts to Cover:
 
 ✅ OOP Principles: Encapsulation, Inheritance, Polymorphism, Abstraction.  
@@ -70,5 +61,3 @@ Basic Concepts to Cover:
 ✅ Database Design: Normalization, Indexing, SQL vs NoSQL.  
 ✅ Microservices & REST APIs: How to design scalable web applications.  
 ✅ Caching & Load Balancing: Redis, CDN, and other optimizations.  
-
----