Regex replacing multiple characters in string.

Question

I have been working through the Java regex tutorial and tried to modify one of the programs for my own use. Basically, I want to take a string and convert the chatracters A to T, T to A, C to G and G-C.
I produced the rather crude program below, but of course it doesn't work. A could be converted to T and back again before the program terminates.
I know that the code to do this correctly is probably quite complex, so could anyone point me in the direction of a tutorial which will help me to do this?
This aside, I take it that if I am looking for multiple matches of characters which won't give the problem already indicated above, my code is too bloated anyway. Say, for example, instead of wanting to replace A to T, T to A, C to G and G-C, I wanted to replace dog-cat, horse-donkey - lion, tiger , cat-mouse. My code will work for this, but I am sure that it could be compressed a lot. Surely I would not need all the lines of code to do this?
Thanks for any help,
Tim
import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.io.*;  // needed for BufferedReader, InputStreamReader, etc.
    /** A Java program that demonstrates console based input and output. */
     class dna {
        // Create a single shared BufferedReader for keyboard input
        private static BufferedReader stdin =
            new BufferedReader( new InputStreamReader( System.in ) );
        // Program execution starts here
        public static void main ( String [] args ) throws IOException
            // Prompt the user
            System.out.print( "Type your DNA sequence: " );
            // Read a line of text from the user.
            String DNA = stdin.readLine();
            DNA = DNA.toUpperCase();
            String DNA2 = DNA;
            //calculate reverse complement
            Pattern A = Pattern.compile("A");
            Pattern T = Pattern.compile("T");
            Pattern C = Pattern.compile("C");
            Pattern G = Pattern.compile("G");
            Matcher AA = A.matcher(DNA);
            DNA = AA.replaceAll("T");
            Matcher TT = T.matcher(DNA);
            DNA = TT.replaceAll("A");
            Matcher CC = C.matcher(DNA);
            DNA = CC.replaceAll("G");
            Matcher GG = G.matcher(DNA);
            DNA = GG.replaceAll("C");
            // Display the input back to the user.
            System.out.println( "DNA input             : " + DNA2);
            System.out.println ("Complementary sequence: " + DNA);
    }

Answer 1

TimM wrote:
Thanks a lot!!! Can't believe you managed all that with so few lines of code.You're welcome.
Must be great to know what you are doing :-)
Thanks again,
TimAfter being a bit more familiarised with the methods of String, you'll be able to do this in no time, I'm sure!