This is a part of my java code, in this code I have written that when I click the button the value of JProgressBar should becomes 0 and stringPainted(); becomes true, but "string painted" is not visible when I click the button, please help.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JProgressBar;





public class R implements ActionListener {


    static int y;
    CustomProgressBar b = new CustomProgressBar();



    public static void main(String arg[]) throws Exception {
        new R();
    }



    public R() throws Exception {
        JFrame f = new JFrame();
        JButton btn = new JButton("Click");
        f.setExtendedState(JFrame.MAXIMIZED_BOTH);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setUndecorated(true);
        f.setLayout(new FlowLayout());
        btn.addActionListener(this);
        f.add(b);
        f.add(btn);
        f.setVisible(true);
    }



    class CustomProgressBar extends JProgressBar{


        private static final long serialVersionUID = 1L;
        private boolean isStringToBePainted = false;
        public CustomProgressBar() {
            super(JProgressBar.VERTICAL,0,100);
        }



        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if(isStringToBePainted ) {
                Dimension size = CustomProgressBar.this.getSize();
                if( CustomProgressBar.this.getPercentComplete()<0.9  )
                    R.y = (int)( size.height - size.height * CustomProgressBar.this.getPercentComplete() );     
                String text = getString();
                g.setColor(Color.BLACK );
                g.drawString(text, 0, R.y);
            }
        }
        @Override
        public void setStringPainted(boolean b) {
            isStringToBePainted=b;
        }
    }



    @Override
    public void actionPerformed(ActionEvent e) {
        b.setValue(0);
        b.setStringPainted(true);

    }

}