My English is not very good, please forgive me!

Changes:
Handling exceptions: The new code introduces a new ExitException class to handle the case where the user types "exit." This is a way of using exceptions to control the flow of the program. If the user types "exit," the getValidNumber and getValidOperator methods throw this exception, which is then caught and handled in the main method. It prints a message and exits the program. This is an improvement over the original code where the "exit" condition was checked in the loop method, which made it harder to follow the flow of the program.
Input Validation: The getValidNumber and getValidOperator methods in the optimized code add some extra checks for user input. If the user enters an invalid number or operator, the program displays an error message and waits for further input, rather than throwing an exception. This is a better user experience than the original code, which didn't validate the operator and could throw a NumberFormatException if the user entered an invalid number.
Code Structure: The optimized Novum.java spreads out the logic across the getValidNumber, getValidOperator, and loop methods, rather than putting all the logic in one method. This makes the code easier to understand and maintain because each method has a clear responsibility. The original code had a single loop method that was responsible for all operations, which made it longer and harder to understand.
Code readability: The optimized Novum.java uses clearer variable names, like firstNumber, secondNumber, and operator, which make the code easier to read. The original code used constants to represent the states of the program, which made it harder to follow.
Separation of Concerns: The optimized code separates the calculation of the result into a separate getResult method, which takes the operator and two numbers as parameters and returns the result. This makes it easier to understand and maintain, as each method has a clear responsibility. In the original code, the calculation was done directly in the loop method, making it longer and harder to understand.