Java 小程序，label 放到 panel 里面，panel 放到 frame 里面，为什么 label 没能显示出来呢？

Question

/**
 *    Filename: tsForJPanel.java
 *     @author: Amitayus
 *    Created : 2013/10/31 19:08:49
 */
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Toolkit;

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

public class TestFor {
	public static void main(String[] args) {
        JFrame jFrame = new JFrame("test for jpanel");
        jFrame.setResizable(true);
        jFrame.setLayout(null);
        Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
	jFrame.setBounds(((int)dimension.getWidth() - 400) / 2, ((int)dimension.getHeight() - 300) / 2, 400, 300);
	jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();
        panel.setLayout(null);
        panel.setPreferredSize(new Dimension(200,150));
		panel.setBackground(Color.CYAN);

        JLabel label1 = new JLabel("姓名");
		label1.setBounds(10, 10, 100, 30);
		panel.add(label1);

        jFrame.add(panel);
        
        label1.setVisible(true);
        jFrame.setVisible(true);
	}
}

Answer 1

没有设置panel的大小和位置