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


class ButtonListener implements ActionListener {
    // each button listener stores the name of the button
    private String text;
    
    // given the text when it's created 
    public ButtonListener(String t) {
        text = t;
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        JOptionPane.showMessageDialog(null, "You pushed button " + text);
    }
}

public class LayoutExample {
    public static void addButton(String text, JFrame f) {
        // add a button object
        JButton button = new JButton(text);
        button.addActionListener(new ButtonListener(text));
        f.getContentPane().add(button);
    }

    public static void main(String[] args) {
        // create and set up the window.
        JFrame frame = new JFrame("Button Example!");

        // make the program close when the window closes
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // create the box layout
        frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));

        // add some buttons
        addButton("A", frame);
        addButton("B", frame);
        addButton("C", frame);
        addButton("D", frame);

        // display the window.
        frame.pack();
        frame.setVisible(true);
    }    
}