新手求助，有关javaGUI的问题，求帮忙！！谢谢

Question

import java.awt.*;
import javax.swing.*;

public class SKK{
public static void main (String[] args){
JFrame frame= new JFrame("啦啦啦");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
int a= (int)(Math.random()*6+1);
int b= (int)(Math.random()*6+1);
int c= (int)(Math.random()*6+1);
int d= (int)(Math.random()*6+1);

    JPanel panel1 =new JPanel();
    //panel1.setPreferredSize(new Dimension(50,100));
    panel1.setBackground(Color.green);
    ImageIcon Icon1=new ImageIcon("die0"+a+".png");
    JLabel label1=new JLabel(Icon1);
    panel1.add(label1);
    ImageIcon Icon2 =new ImageIcon("die0"+b+".png");
    JLabel label2=new JLabel(Icon2);
    panel1.add(label2);

    JPanel panel2 =new JPanel();
    //panel1.setPreferredSize(new Dimension(50,100));
    panel2.setBackground(Color.red);
    ImageIcon Icon3=new ImageIcon("die0"+c+".png");
    JLabel label3=new JLabel(Icon3);
    panel2.add(label3);
    ImageIcon Icon4=new ImageIcon("die0"+d+".png");
    JLabel label4=new JLabel(Icon4);
    panel2.add(label4);

    JPanel panel =new JPanel();
    panel.setBackground(Color.pink);
    panel.add(panel1);
    panel.add(panel2);

    frame.getContentPane().add(panel);
    frame.pack();
    frame.setVisible(true);

}

}

Answer 1

如果固定了面板的大小，就变成了第一张图那样，不固定面板就能完整的显示出来，就像第二张图。为什么？