我如何在Jframe中分离Jpanel

我正在尝试实现这种布局

我不知道为什么我得到这个

这是我的代码

package testing;

import java.io.*;
import java.util.*;
import java.security.*;
import javax.xml.bind.DatatypeConverter;
import java.lang.*;
import java.awt.*;
import javax.swing.*;

public class Testing 
{


    public static class GridPanel extends JPanel 
    {
        public GridPanel()
        {
            setLayout(new GridLayout(4,4));
            setBackground(Color.GREEN);
            this.setPreferredSize(new Dimension(500,100));



            JButton b1 = new JButton ("Button 1");
            JButton b2 = new JButton ("Button 2");
            JButton b3 = new JButton ("Button 3");
            JButton b4 = new JButton ("Button 4");
            JButton b5 = new JButton ("Button 5");
            JButton b6 = new JButton ("Button 6");
            JButton b7 = new JButton ("Button 7");
            JButton b8 = new JButton ("Button 8");
            JButton b9 = new JButton ("Button 9");
            JButton b10 = new JButton ("Button 10");
            JButton b11 = new JButton ("Button 11");
            JButton b12 = new JButton ("Button 12");
            JButton b13 = new JButton ("Button 13");
            JButton b14 = new JButton ("Button 14");
            JButton b15 = new JButton ("Button 15");
            JButton b16 = new JButton ("Button 16");

            add(b1);
            add(b2);
            add(b3);
            add(b4);
            add(b5);
            add(b6);
            add(b7);
            add(b8);
            add(b9);
            add(b10);
            add(b11);
            add(b12);
            add(b13);
            add(b14);
            add(b15);
            add(b16);

        }

    }



    public static void main(String[] args) 
    {
         JPanel primary = new JPanel();
         primary.setPreferredSize(new Dimension(500,500));



        JPanel jp1 = new JPanel();
        jp1.setPreferredSize(new Dimension(500,100));
        JTextField jt1 = new JTextField(8);
        jp1.add(jt1);


       GridPanel gp = new GridPanel();

       primary.add(jp1);
       primary.add(gp);

       JFrame jf = new JFrame();
       jf.setPreferredSize(new Dimension(500,500));
       jf.add(primary);
       jf.pack();
       jf.setVisible(true);

    }


}

我不确定如何将框架中的两个面板分开，我做错了什么？