Which three are advantages of the Java exception mechanism?

Given the code fragment:

What is the result?

Given the code fragment:

Test.java:

Which is the result?

Given the code fragments:

What is the result?

Given these two classes:

Any amount of electricity used by a customer (represented by an instance of the Customer class) must contribute to the customer's bill (represented by the member variable bill) through the useElectricity method.
An instance of the Customer class should never be able to tamper with or decrease the value of the member variable bill.
How should you write methods in the ElectricAccount class at line n1 so that the member variable bill is always equal to the value of the member variable kwh multiplied by the member variable rate?