// read from file
        try{
            BufferedReader bf = new BufferedReader(new FileReader(fname));
            String s;
            while((s = bf.readLine()) != null){
                Print.p(s);
            }
            bf.close();
        }catch(IOException e){
        }

        // write to file
        String fname =  "/tmp/bst.txt";
        try{
            BufferedWriter bw = new BufferedWriter(new FileWriter(fname));
            bw.write("123\n");
            bw.close();

        }catch(IOException io){
            Print.p("Ex" + io.getMessage());
        }