Why I should define a JLabel before a addActionListener?

Why I should define a JLabel before a addActionListener?

I have one JLabel and one JButton into JFrame. I write code for
actionPerformed event of JButton like following:
btnOK.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
lblA.setText("Hello"); // error here
}
});
final JLabel lblA = new JLabel("");
but i get following error:
lblA cannot be resolved
however if I placed define of JLabel before addActionListener like
following my problem solved:
final JLabel lblA = new JLabel("");
btnOK.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
lblA.setText("Hello"); // error here
}
});