Welcome to the Ranch
I added
code tags to your post. Always use them, and think how much better still it would have been with consistent indentation
Look at line 22 for example.
I think
you should go back to work out the algorithm for turning things into ACTG. Why have you got those Strings "00"? If they represent numbers, why are you not using numbers? Why haven't you got a Nucleotide class with four instances (that is called an
Enumerated Type) A C T G? Show us what you think the algorithm should be for determining the four letters, then if you want to add something to a text component, you will find it quite easy with
methods of text components.
Don't use += for Strings. Least of all in a loop, because you get slow execution. Use a StringBuilder for that sort of thing.