Refactor Hotel Management System Code for Improved Readability and Maintainability

[PritishDoc]

Class Structure and Design:
The holder class should follow Java naming conventions (e.g., Holder instead of holder).
Encapsulation should be implemented to protect the data in classes like Singleroom, Doubleroom, and holder.

Code Duplication:
There is significant duplication in methods such as bookroom, deallocate, order, and bill. These methods should be refactored to reduce redundancy and improve maintainability.

Exception Handling:
The current exception handling is minimal and does not provide meaningful error messages or recovery options. More specific exceptions and error handling should be implemented.

Magic Numbers:
The use of magic numbers (e.g., room numbers in bookroom, deallocate, order, and bill methods) should be avoided. These should be replaced with constants or enumerations.
Input Validation:

Input validation is lacking in several areas, which could lead to runtime errors. Input validation should be added to ensure robustness.
Switch Cases:

The switch statements in CustDetails, bookroom, features, availability, and bill methods are extensive and can be simplified or refactored using more modern design patterns like the strategy pattern.
Serialization:

The serialization logic is embedded in the main class and the write class. Consider creating a separate utility class for handling serialization and deserialization.

Thread Safety:
Ensure that the code is thread-safe, especially with regard to the shared holder object.

• Consider using modern Java features and design patterns to refactor the code. Adding unit tests would also be beneficial to ensure that the refactored code works as expected.