Question

public class MainFrame extends JFrame {
    MainFrame()
    {
        JButton zeroButton = new JButton("0");
        add(zeroButton);

        Handler handler = new Handler();
        zeroButton.addActionListener(handler);
    }

    private class Handler implements ActionListener
    {

        public void actionPerformed(ActionEvent e) {
              if (e.getSource() == **zeroButton**)
                  JOptionPane.showMessageDialog(null, "hello there!");
        }
    }
}

The code has an error which underlines what I marked as bold in the code.
here is the error message: “cannot find symbol”

I thought I can access outer class modifiers from the inner class, but it doesn’t work!

Answer 1

zeroButton is not a member of outer class (MainFrame), it’s a local variable in MainFrame constructor.

Try something like this

public class MainFrame extends JFrame {
    private final JButton zeroButton;

    MainFrame() {
        zeroButton = new JButton("0");

PS I’m also not sure if you’re supposed to compare controls with ==. (never used swing)