When I entered non-numeric input for the bet, it deducts my tokens and starts spinning the slot machine. Non-numeric input should be regarded as invalid input and requires player to enter numeric input.
Problem resolved by prohibiting player to enter input by themselves, but allow them to input the bet by clicking the add or minus button.
The problem is caused by Generics in Java is only available at compile time. Java generic is only performing type safe casting at compile time. However, the problem is caused by user enter inputs at run time. Therefore, disabling the editable feature in spinner is the most intuitive way to solve the problem.