Output number is wrong when inputing number w/commas

Question

I've been working on this code for less than a week and have been able to make it work like I need it to except when I input numbers with commas (the loan amount) or I'll get an error when I type in "%" for the interest. Any ideas on what I've done wrong to fix these two errors? I thought the while statement was the problem for the comma error, but that part was given to me so it shouldn't be wrong. Any and all help would be much appreciated. Thanks in advance.
BTW, it compiles just fine and will do what I want it to if I leave off the commas and the "%" sign... but the instructions are to enter both the commas and "%" as part of the inputs.
I think this is where the code goes awry... but I'm not sure.
          // Substrings
          principalAmount = principalAmount.substring(principalAmount.indexOf('$')+1);
          principalAmount = principalAmount.substring(principalAmount.indexOf(',')+1);
          interestAmount = interestAmount.substring(interestAmount.indexOf('%')+1);
          interestAmount = interestAmount.substring(interestAmount.indexOf('.')+1);
          // convert string to #
          principal = Double.parseDouble(principalAmount);
          interest = Double.parseDouble(interestAmount);
          interest = interest / 100;
          years = Integer.parseInt(yearsAmount);
          // While statement
          while (principalAmount.indexOf(',') >= 1)
               principalAmount = principalAmount.substring(0,principalAmount.indexOf(','))
               + principalAmount.substring(principalAmount.indexOf(',')+1);
          

Answer 1

@flounder
Isn't that what I'm doing by using the substrings? Sorry, I'm a bit confused on how to strip out and calling the parseDouble.
@CaptainMorgan08
I was told that by someone else... but I haven't learned what that is yet. In my book, that's in chapter 9, but I've only gotten to chapter 4...
Message was edited by:
Tsurara