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.

Don't you prog-ramers realize that the original poster (OP) wrote as follows:
"I'm trying to read in a list of strings of characters A, C, G,and T"

Duh! Could it be that he (or she) OP is referring to:
A -- Adenine;
C -- Cytosine;
G -- Guanine;
T -- Thymine? As in
http://en.wikipedia.org/wiki/ACGT
which describes the amino-acid building-blocks of DNA?

Now, does anybuddy know who the people are in this picture:
http://www.flickr.com/photos/jurvetson/8663952985