Once again (we saw this in the Chain of Responsibility pattern), a snack vending machine is an example of the State pattern in everyday life. Vending machines have different states and react differently depending on the amount of money that we insert. Depending on our selection and the money we inserted, the machine can:
Reject our selection because the product we requested is out of stock
Reject our selection because the amount of money we inserted is not sufficient
Deliver the product and give no change because we inserted the exact amount
Deliver the product and return the change
There are, for sure, more possible states, but you get the point. The following figure, provided by www.sourcemaking.com [j.mp/smstate], shows a possible implementation of the different vending machine states using inheritance:
