Java throw 2 exceptions

Hello! I have completed a class for PostFix expression but right now I need to handle 2 type of exceptions. I have 2 methods in that class (toString and Evaluate) and both method are working. However, you will need to write : 1.1) IllegalArgumentsExceptions in the constructor to handle the case of an illegal string examples : " 3 5 +++", "hello", "4 5 6 3 2". A correct input can be "4 9 /", "4 8 3 + /", " a b +". We don't have to handle parenthesis here. 1.2) Another exception in the Evaluate method because for that method we can not evaluate string that contain letters such as " a b +" since we don't know the value of a and b (but it's correct for the constructor). So it's the same logic as the constructor but without letters/variables names. You will probably need to REGEX to read the expression. I think it's about 5 lines of code for the evaluate method and a bit more for the constructor