import java.awt.*;import javax.swing.*;public class FrameTest{public static void main(String[] args){EventQueue.invokeLater(new Runnable(){public void run(){JFrame frame = new SimpleFrame();frame.setUndecorated(true);frame.setResizable(true);frame.setTitle("AAAAAAAAA");frame.toFront();frame.setExtendedState(Frame.MAXIMIZED_BOTH);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setVisible(true);}});}}class SimpleFrame extends JFrame{public SimpleFrame(){add(new Content());pack();Toolkit kit = Toolkit.getDefaultToolkit();Dimension screenSize = kit.getScreenSize();int screenWidth = screenSize.width;int screenHeight = screenSize.height;setSize(screenWidth/2,screenHeight/2);setLocationByPlatform(true);Image image = Toolkit.getDefaultToolkit ().getImage ("C:\\Users\\Asuna\\Pictures\\00010.JPEG");setIconImage(image);}}class Content extends JComponent{public static final int MESSAGE_X = 75;public static final int MESSAGE_Y = 100;private static final int DEFAULT_WIDTH = 300;private static final int DEFAULT_HEIGHT = 200;public void paintComponent(Graphics g){g.drawString("BBBBBBBBBBBBBBBBBB",DEFAULT_WIDTH/2,DEFAULT_HEIGHT/2);}public Dimension getPreferredSize(){return new Dimension(DEFAULT_WIDTH,DEFAULT_HEIGHT);}}為什么用上frame.setUndecorated(true); 這個方法就會報錯 不就只是把標題欄去掉嗎