Java Alert Message

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

class  Validation{
    public static void main(String[] args){
        JFrame f=new JFrame();
        f.setLayout(null);
        final JRadioButton radio=new JRadioButton("Select");
        final JCheckBox  check=new JCheckBox("Check");
        JButton b=new JButton("Check");
        b.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
            if(radio.isSelected()&&!check.isSelected()){
                JOptionPane.showMessageDialog(new JFrame(), "You have selected radiobutton istead of checkbox", "Dialog",
        JOptionPane.ERROR_MESSAGE);
            }
            }
        });
   radio.setBounds(10,10,100,20);
   check.setBounds(10,40,100,20);
   b.setBounds(10,70,100,20);
   f.add(radio);
   f.add(check);
   f.add(b);
   f.setVisible(true);
   f.setSize(300,140);
        }

}