import java.io.File;
import java.io.RandomAccessFile;
public class Main {
public static void main(String[] argv) throws Exception {
File f = new File("filename");
RandomAccessFile raf = new RandomAccessFile(f, "rw");
// Read a character
char ch = raf.readChar();
// Seek to end of file
raf.seek(f.length());
// Append to the end
raf.writeChars("aString");
raf.close();
}
}