This lab will help you learn how to handle exception (i.e., error) in your code gracefully.

The objectives of this week are following:

• Simple Data encapsulation and data validation.
• Simple collection API (ArrayList)
• Exception Handling

To complete the lab you need to meet following requirements:

• Write the classes according the specifications.
• Write a readable, sensible, usable, beautiful code.
• Pass all the unit tests.

Requirement:

1. For floating point number, only the five digits after dot will be considered in the result. The sixth and so on digit should be rounded to the nearest number, 5 will be always round up.

2. Only the arguments with non-negative value will be computed, otherwise, RuntimeException should be thrown from operators.

3. For division operation, it must throw an ArithmeticException when divide by zero.

4. For username, it has to be alphanumeric only, no symbols. The first character must be an english alphabet. The username has to be at least eight character in length. The method setUserName() must return the previous user name, if any, or null. RuntimeException should be thrown if an invalid name is assigned.

5. For password, it has to be alphanumeric only, no symbols. There must be at least one number and one english alphabet in the password. Also there must be at least one capitalized character and one non-capitalized character. The length must be at least 12. The method setPassword() must return the length of the new password. RuntimeException should be thrown when an invalid password is assigned.

6. For Users class, deleteUser must throw runtimeException when deleting user does not exists.