Java Programming

Hello everyone

I am relative novice to Java, I have procedural C programming background.

I am reading many very large (many GB) comma/double-quote separated ASCII CSV text files and performing various kinds of pre-processing on them, prior to loading into the database.

I am using Java7 (the latest) and using NIO.2.

The IO performance is fine.

My question is regarding performance of using char[i] arrays versus Strings and StringBuilder classes using charAt() methods.
I read a file, one line/record at a time and then I process it. The regex is not an option (too slow and can not handle all cases I need to cover).

I noticed that accessing a single character of a given String (or StringBuilder too) class using String.charAt(i) methods is several times (5 times+?) slower than referring to a char of an array with index.

My question: is this correct observation re charAt() versus char[i] performance difference or am I doing something wrong in case of a String class?

What is the best way (performance) to process character strings inside Java if I need to process them one character at a time ?

Is there another approach that I should consider?

Many thanks in advance