import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class SecondGUI extends JFrame {
    public static void main(String[] args) {
        // new SecondGUI().setVisible(true);
        new SecondGUI();
    }
    public SecondGUI(){
        super("SecondGUI");
        JButton b1,b2,b3;
        getContentPane().setLayout(new FlowLayout());
        getContentPane().add(b1 = new JButton("B1"));
        getContentPane().add(b2 = new JButton("B2"));
        getContentPane().add(b3 = new JButton("B3"));
        b1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(b1, "B1");
            }   
        });
        b2.addActionListener( e -> JOptionPane.showMessageDialog(b1, e.getActionCommand()) );
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }
}