Java Swing Access Class Variables From Button

Question

So in my Java Swing application, I need a button ActionListener to be able to access variables outside of its scope like so:

int x = 13;

JButton btn = new JButton("New Button");
btn.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        System.out.println(x);
    }
});

but I get a variable out of scope error. How can I access it?

Answer 1

The action listener is an anonymous inner class. This means that it can only use final variables from an outer scope. So, either declare x as final or pass it into the class some other way.

This should work:

final int x = 13;

JButton btn = new JButton("New Button");
    btn.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        System.out.println(x);
    }
});

Alternatively, see Pass variables to ActionListener in Java for some other options.