如何从JTextField中读取System.in

Question

I am trying to make System.in InputStream read from a JTextField.

What i need it to do, is to allow .read() to proceed once a user presses enter in a JTextField with a String in it.

The issue is that I don't know when .read() will be invoked, and i want it to block without freezing the main thread, until enter is pressed by the user in the JTextField where it will notify the thread waiting.

So far i tried the following:

public class InputStreamHandlerThread extends Thread {

    private JTextField txt;
    public InputStreamHandlerThread(JTextField txt) {
        this.txt = txt;
        start();
    }

    @Override
    public void run() {
        System.setIn(new FakeInputStream());
    }

    class FakeInputStream extends InputStream {
        private int indx = 0;

        @Override
        public int read() throws IOException {
            if (indx == txt.getText().length()) {
                indx = 0;
                try {
                    synchronized (this) {
                        wait();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            int byt = txt.getText().getBytes()[indx];
            indx++;
            return byt;

        }
    }
}

which is initialized and started by the GUI thread. So once the GUI loads, it creates an instance of this class and keeps a pointer so that when the enter key is pressed on the keyboard within the JTextField, it is notified to read from it.

       in = new JTextField();
       in.addKeyListener(new KeyAdapter() {
            @Override
            public void keyTyped(KeyEvent a) {
                if (a.getKeyChar() == '\n') {
                    inputStreamHandler.notify();
                }
            }
        });

So currently there are three threads:
1. The main thread on what the GUI runs on
2. The InputStream handler thread (See above ^)
3. The thread that reads from System.in

The problem is that once i invoke inputStreamHandler.notify(); it throws a java.lang.IllegalMonitorStateException which according to the docs, is thrown if the thread is not the holder of the lock. How do i resolve this?

Thank you :-)

Answer 1

String text;

...

in.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e){
        text = in.getText();
    }
});

Make sure you make text and in both fields.