Shopping Cart – Part 5

Goal: Quality control the Cart class.

Unchecked exceptions

An unchecked exception crashes the app as a result of badly written code.

You should throw an:

• IllegalArgumentException when the caller passes faulty arguments into a method/constructor.

• IllegalStateException when an object calls its method at a "bad time" (object not in a legal state).

Throwing an unchecked exception forces the caller to improve their code.

Task 1 – Inspecting the Cart class

1. The constructor doesn't receive any parameters so there's nothing to check.

2. Should the setItem setter check for a null? No.

   • The code would already throw a NullPointerException. So, throwing an IllegalArgumentException would be redundant.

3. Should the add method check for a null? No.

   • For the same reason as before.

4. Should the remove method check for a null? No.

   • For the same reason as before.

5. Is there a need to throw an IllegalStateException anywhere? Yes, in two places.

• If the items ArrayList is empty, the store is not in a valid state to call the remove method.

• If the items ArrayList is empty, the store is not in a valid state to call the checkout method.

That's all!

You added checkpoints to the Cart class. The checkpoints forbid the caller from misusing the remove and checkout methods.