Untitled

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

public class GUI implements ActionListener {
    JFrame frame = new JFrame();

    JPanel buttonPanel = new JPanel();
    JButton addButton = new JButton("Add");

    int cnt = 1;

    public GUI () {
        buttonPanel.setBounds(0, 0, 600, 600);

        buttonPanel.setLayout(new FlowLayout());
        buttonPanel.add(addButton);
        addButton.addActionListener(this);

        frame.add(buttonPanel);

        frame.setSize(600, 300);
        frame.setLayout(null);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        buttonPanel.add(new JButton("B" + cnt));
        cnt++;
        frame.setVisible(true);
    }
}