单纯从语法角度来看，下面这段java代码有问题吗，为什么编译的时候会出现少分号的提示

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Response implements ActionListener {
public static void main(String args[]) {
JFrame w = new JFrame();
w.setSize(200, 400);

    @Override
    public void actionPerformed(ActionEvent arg0) {

    }

        w.setVisible(true);
}

}