为什么hello world在内容窗格上显示不出来
import java.awt.*;
import javax.swing.*;
public class HW
{
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
HWFrame frame = new HWFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.setTitle("Hello World");
frame.setSize(300,200);
}
});
}
}
class HWFrame extends JFrame
{
public void HWFrame()
{
HWPanel panel = new HWPanel();
add(panel);
}
}
class HWPanel extends JPanel
{
public void paintComponent(Graphics g)
{
g.drawString("Hello,World!",75,100);
}
}