Cannot refer to a non-final variable

I'm trying to create simple GUI program in Java and I couldn't find a proper solution to error cannot refer to a non-final variable inside an inner class defined in a different method.

Here's my small code so far;

myP开发者_开发问答anel = new JPanel();

JButton myButton = new JButton("create buttons");
myButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        int val = Integer.parseInt(textfield.getText());
        for(int i = 0; i < val; i++) {
            JButton button = new JButton("");
            button.setText(String.valueOf(i));
            button.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    clickButton(i);
                }
            });
            myPanel.add(button);
            myPanel.revalidate();
        }
    }
});

Maybe my approach is completely wrong. What I'm trying to do is; I want to create a set of buttons and say when the user presses a button I want to display a message like "you pressed the button 4", or "you pressed the button 10".

i has to be final in order for the inner class to access it. You can work around this by copying it to a final variable.

But I'd recommend refactoring the contents of the for loop into a separate method like this:

for(int i = 0; i < val; i++) {
    myPanel.add(makeButton(i));
    myPanel.revalidate();
}

...

private JButton makeButton(final int index) {
    JButton button = new JButton("");
    button.setText(String.valueOf(index));
    button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            clickButton(index);
        }
    });

    return button;
}

To avoid this problem, you have to either declare the myPanel as a member variable of the class or use something else that refers to the member of the class.

Anonymous class can only use local variables declared as final so that they are guaranteed not to change.