Adicionando campo em tempo de execução

import java.awt.Dimension;
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.JTextField;

public class Teste extends JFrame{
	
	public Teste() {
		this.setTitle("Teste botão dinâmico");
		this.setLayout(new FlowLayout(FlowLayout.LEFT));
		JTextField field = new JTextField();
		field.setPreferredSize(new Dimension(300, 25));
		
		JButton button = new JButton("OK");
		button.setPreferredSize(new Dimension(50, 25));
		button.addActionListener(new ActionListener() {
			
			@Override
			public void actionPerformed(ActionEvent e) {
				JButton b1 = new JButton("Botão dinâmico");
				b1.setPreferredSize(new Dimension(100, 25));
				Teste.this.add(b1);
				Teste.this.pack();
			}
		});
		
		this.add(field);
		this.add(button);
		this.pack();
		this.setLocationRelativeTo(null);
		this.setVisible(true);
	}
	
	public static void main(String[] args) {
		new Teste();
	}
	
}