即使在同一类中声明了对象也无法找到对象

Question

I'm currently learning how to build GUI's in Java and I'm encountering the following error "cannot find symbol - Class Listener".

The following code creates radio buttons and then pairs them with a JLabel and an action listener. However even though I provide listener as an argument to button, the compiler is telling me it cannot find the listener class. Does anyone know why this is?

The error is occuring on the parameter line of the button method. Any assistance is greatly appreciated.

private void build(Stadium stadium)
    {  

       Listener listener = new Listener();

       add(button("Front", listener));
       add(button("Middle", listener));
       add(button("Back", listener));

    }

    private JRadioButton button(String label, Listener listener)
    {   JRadioButton button = new JRadioButton(label);
        button.addActionListener(listener);
        group.add(button);
        return button;  }

Answer 1

Use ActionListener not Listener , their is nothing like Listener in GUI.

private void build(Stadium stadium)
{  

   ActionListener listener = new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            //Here you implement what you want your listener to execute on  button click;
        }
    };

   add(button("Front", listener));
   add(button("Middle", listener));
   add(button("Back", listener));

}

private JRadioButton button(String label, Listener listener)
{   JRadioButton button = new JRadioButton(label);
    button.addActionListener(listener);
    group.add(button);
    return button;  }

Answer 2

You need an ActionListener, not a Listener. Your class should implement ActionListener ( public class GUI implements ActionListener { )

and then implement the actionPerformed method.

add the instance of this class as listener.

Answer 3

您可能需要导入Listener