why the while does not stop at the second loop

Question

At the first loop while stops and waits for console input at the incomStr = view.read(); but at the second loop it doesn't stop, reads null and goes on.

Why is it happening?

public void mainDialogueHolder() {//todo

        setCmdState(CmdLineState.WAIT);
        view.write("Hello, user!");
        view.write("Please, type `help` for list available commands. ");
        while (getCMDState().equals(CmdLineState.WAIT)){
            String incomStr;
            incomStr = view.read();//implementation is below
            readCmd(incomStr);
        }
    }

Implementation of view

public class Console implements View {

    @Override
    public void write(String message) {
        System.out.println(message);
    }

    @Override
    public String read() {
        try (
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))
        ){
            return reader.readLine();
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
            return null;
        }
    }
}

If it return `null`, it means you go through your `catch` block.Then what is the message prompted, that should tell what is the error — vincrichaud, Jun 19 '18 at 08:33
but why it does not stop and wait at return reader.readLine(); — Олександр Козачок, Jun 19 '18 at 08:49

score 0 · Accepted Answer · answered Jun 19 '18 at 09:38

Well it looks like your try with resource closes the System.in by closing the BufferedReader, which in turn will close it's Reader (InputStreamReader) and that one closes System.in. The System.in is final static, hence once you close it you wouldn't be able to use it again as it's not possible to reopen it. Well what do I do then If I can't close it ? Perhaps you could write a wrapper like it was suggested here In Java is it possible to re-open System.in after closing it

Yes it is. When I write usual try-catch then it works. Thanks for everybody — Олександр Козачок, Jun 19 '18 at 10:18

why the while does not stop at the second loop

1 Answers1