下列代码说法正确的是( ) import java.awt.FlowLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JButton; import javax.swing.JFrame; public class E extends JFrame{ JButton b; public E() { setLayout(new FlowLayout()); b=new JButton("yes"); setSize(200, 100); add(b); b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { b.setText("ok"); } }); } public static void main(String[] args) { new E().setVisible(true); } }