To expand upon Mr. Eels comment, you can do it like this:
File file = new File("C:\\A.txt");
FileWriter writer;
try {
writer = new FileWriter(file, true);
PrintWriter printer = new PrintWriter(writer);
printer.append("Sue");
printer.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Don't say we ain't good to ya!