swing做的界面，为啥要拖动边框才能显示里面的内容？？
代码如下：
package frames;

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Label;
import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class GameFrame extends JFrame {

/**
* 
*/
private static final long serialVersionUID = 1L;

static final Random random = new Random();

static final StringBuffer sb = new StringBuffer("");

static private int charCounter = 1;

static JFrame frame = new JFrame();

static JPanel panel = new JPanel();

static String letters;

static Label[] labels = new Label[11];

static Timer timer = new Timer();

public GameFrame() {

frame.setBounds(200, 200, 600, 200);

frame.setLayout(new FlowLayout());

panel.setBackground(Color.YELLOW);

panel.setSize(200, 100);

timer.schedule(new TimerTask() {

@Override
public void run() {

panel.removeAll();

letters = makeLetter();

for (int i = 0; i < letters.length(); i++) {

labels[i] = new Label(letters.charAt(i) + "");

System.out.println(labels[i].getText());

panel.add(labels[i]);



}
}
}, 0, 3000);

frame.getContentPane().add(panel);

frame.setDefaultCloseOperation(3);

frame.setVisible(true);

}

public static String makeLetter() {

sb.delete(0, sb.length());

for (int i = 0; i < charCounter; i++) {

int ranNum = random.nextInt(26);

char character = (char) (ranNum + 'A');

sb.append(character);
}

charCounter++;

return sb.toString();

}

}


------解决方案--------------------
可能是窗口太小，或者是layout的问题