Question

I have trying for a while now to access a variable in my main class:

public class Results extends JFrame {
     public static void main(String[] args) 
     {
        System.out.println(doble);
     }}

which is inside an actionlistener, like this

public Results ()
{
 // Create a JPanel for the buttons DOUBLE AND NOT DOUBLE
    JPanel duplicate = new JPanel(
    new FlowLayout(FlowLayout.CENTER));
    JButton doblebutton = new JButton("DOUBLE");
    doblebutton.addActionListener(new ActionListener(){
    private int doble;
    public void actionPerformed(ActionEvent ae){
                doble++;
                System.out.println("Doubles: " + doble);
                }
  });
}

I have tried like 5 ways to do it, but it doesn’t seem possible. Any thoughts?

Answer 1

Try moving your declaration of doble outside of the constructor so that it becomes a field, like this:

public class Results extends JFrame {

    private int doble;

    public Results() {
        // Create a JPanel for the buttons DOUBLE AND NOT DOUBLE
        JPanel duplicate = new JPanel(new FlowLayout(FlowLayout.CENTER));
        JButton doblebutton = new JButton("DOUBLE");
        doblebutton.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent ae) {
                doble++;
                System.out.println("Doubles: " + doble);
            }
        });
    }

    public static void main(String[] args) {
        Results results = new Results();
        System.out.println(results.doble);
    }

}

Some comments:

• Since doble is a non-static field, you need to access it using a concrete instance of Results. Look at the change I made to your main() method.
• Accessing a private field directly like this doesn’t indicate very clean encapsulation and in fact generates compiler warnings.
• Using a non-word doble to avoid the compiler error on the reserved word double is probably not as nice as something more meaningful like count

Hope this helps.