Execution terminates even when exception is caught

Question

I was running a simple Calculator app to learn Java\'s exception handling. I\'ve set two exceptions to be handled: InputMismatchException and ArithmeticException for divisio

Answer 1

InputMismatchException is caused by the call to nextInt(), because the next token is 4+5.

The token is not consumed by the failed call.

Which means that OP = input.next().charAt(0) sets OP = '4', something that should be very apparent if you debugged the code. See What is a debugger and how can it help me diagnose problems? and How to debug small programs.

You need to discard the failed token(s), e.g. by calling nextLine() in the catch clause:

} catch (InputMismatchException e) {
    System.err.println("Please space out the expression");
    input.nextLine(); // Discard input(s)
} ...