import java.awt.Button;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Registration extends JFrame implements ActionListener {

    JFrame f;
    JPanel p;
    JTextField t1;
    JButton b1;

    public Registration() {
        f = new JFrame();
        f.setPreferredSize(new Dimension(400, 400)); // size of JFrame

        p = new JPanel();
        f.add(p);

        t1 = new JTextField(8);

        p.add(t1);

        b1 = new JButton("check"); // creating a JButton
        b1.addActionListener(this); // adding action listener
        p.add(b1); // adding JButton to panel

        f.pack();

        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        new Registration();

    }

    @Override
    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == b1) {
            if (t1.getText().length() == 10 && t1.getText().matches("[0-9]+")) { // validate
                                                                                    // the
                                                                                    // string
                JOptionPane.showMessageDialog(f, " valid string");
            } else {
                JOptionPane.showMessageDialog(f, " Invalid string");

            }

        }
    }

}