Converting Hexadecimal String to Decimal Integer

Question

I wrote some code to convert my hexadecimal display string to decimal integer. However, when input is something like 100a or 625b( something with letter) I got an error like

Answer 1

Google got me here, so i am updating this late for other to find when searching. A much simpler way is to use BigInteger, like so:

BigInteger("625b", 16)