Java swing disable button

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class DisableButton{
    public static void main(String[] args){
    JFrame f=new JFrame();
    JLabel label=new JLabel("Account Number: ");
    final JTextField text=new JTextField(20);
    final JButton b=new JButton("Check");
    text.addKeyListener(new KeyAdapter(){
        public void keyReleased(KeyEvent e){
        String value=text.getText();
        if(value.startsWith("774")||value.startsWith("775")){
            b.setEnabled(false);
            }
            else{
            b.setEnabled(true);
            }
        }
    });

        JPanel p=new JPanel(new GridLayout(2,2));
        p.add(label);
        p.add(text);
        p.add(b);
        f.add(p);
        f.setVisible(true);
        f.pack();
    }
}