Running an application from java

Question

Hi all,
Can someone help with this. It is a calculator application using the unix bc calculator program to evaluate the expression.
I get no results form this code. The application hangs. Where have I gone wrong.
public void calculate() {
        try {
            exp.append("\\r\\n");   // add carriage return to the end of the expression
            Process p = Runtime.getRuntime().exec
                    ("bc -qi");
            BufferedWriter output = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
            BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
            output.write(exp.toString());
            while ((result = input.readLine()) != null) {
                System.out.println(result);
            input.close();
            p.destroy();
        } catch (Exception err) {
            err.printStackTrace();
    }thanks,
Sebastian

Answer 1

Thanks.
changing to
exp.append("\n");and flushing the writer stream and closing the stream fixed the problem.
Why do we have to flush the stream?
and, why do we have to close the writer before reading? what if I want to continue writting in to the writer?
thanks again.