填空题 仔细阅读下面的程序代码，请将划线上①～④的语句补充完整。 import java.awt.*; import java.awt.event.*; public class MyFrameCanExit extends Frame implements ① { public MyFrameCanExit(String str){ super(str); } public void windowClosing( ② e) { System.exit(0); } public void windowClosed(WindowEvent e) { } public void windowOpened(WindowEvent e) { } public void windowIconified(WindowEvent e) { } public void windowDeiconified(WindowEvent e) { } public void windowActivated(WindowEvent e) { } public void windowDeactivated(WindowEvent e) { } public static void main(String args[ ]){ MyFrameCanExit fr = new MyFrameCanExit("Hello !"); fr. ③ (fr); //注册窗口事件监听器。 fr. ④ (200,200); fr.setVisible(true); }