Question

I’ve written a GUI program and I’m not sure what I’m doing wrong. When I run the program, it just quits almost instantly. Hope you can help, here’s the program:

public class RandomGame extends JFrame {
    private JTextField t1 = new JTextField();
    private double t1num = Double.parseDouble(t1.getText());


    public RandomGame() {
        setLayout(new FlowLayout());
        Event1 e1 = new Event1();
        t1.addKeyListener(e1);
        add(t1);

    }


    public class Event1 implements KeyListener {
        @Override
        public void keyPressed(KeyEvent arg0) {
            Random r = new Random();
            switch (arg0.getKeyCode()) {
            case KeyEvent.VK_ENTER:
                if(t1num == r.nextInt()) {
                    t1.setText("You Won!");
                }
                else {
                    t1.setText("You Lost.");
                }

                }
            }



        @Override
        public void keyReleased(KeyEvent arg0) {
            // TODO Auto-generated method stub

        }
        @Override
        public void keyTyped(KeyEvent arg0) {
            // TODO Auto-generated method stub

        }
    }
    public static void main(String[] args) {
        RandomGame gui = new RandomGame();
        gui.setDefaultCloseOperation(EXIT_ON_CLOSE);
        gui.setSize(1280, 800);
        gui.setTitle("Random Game");
        gui.setVisible(true);

    }
}

(Don’t worry about the imports, I just haven’t included them)
Any help would be appreciated.

Answer 1

A NumberFormatException is thrown on startup on this line:

private double t1num = Double.parseDouble(t1.getText());

as the JTextField t1 will contain an empty String.

In fact, this can be simply left unassigned and will take the default 0 value used for numeric primitives.

---

Additionally when using Random

t1num == r.nextInt();

could be written as:

t1num == r.nextDouble();

Also KeyListener is not recommended for use with JTextComponents. Here you simply require the ENTER key action to be handled so an ActionListener would be better & simpler to use.