Hi Cathymala:
Remember that when you are passing objects as arguments, you are passing it by reference, so in the FizzSwitch method, you have the x, and z Fizz variables are refering to the same object, so if you are modifying the values in z or even x, you also are modifying the values in f1. Check this printing the value of f1.x before the f1==f3 statement.
Regards,
Alejandro Galvan
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Preparing
SCJP