Java Swing - 如何当创建JFrame时将焦点设置为JTextField

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;
import javax.swing.JTextField;

class MyFrame extends JFrame {

  JTextField field1;

  public MyFrame() {
    field1 = new JTextField(10);
    getContentPane().add("Center", field1);
    addWindowListener(new WindowAdapter() {
      public void windowOpened(WindowEvent e) {
        field1.requestFocus();
      }
    });
    pack();
    setVisible(true);
  }

}

public class Main {
  public static void main(String[] argv) {
    MyFrame myFrame = new MyFrame();
  }
}