JAVA help (not trolling) (pls)

I'm trying to read in a list of strings of characters A, C, G,and T (ignoring case), and to ignore the rest of the string if it contains any other character.

how do I code this? do I use indexOf?

V new to Java yes. Not trolling just need help quickly.

>>3
Horrible. That code is kind of like your mom. Slow and ugly.