我的ScrollPane里的东西为什么显示不出来？（新手刚练java）求指点

Question

package 点餐;import java.awt.BorderLayout;
import java.awt.Toolkit.*;
import java.awt.event.*;
import javax.swing.*;public class orderform extends logo implements ActionListener
{
JPanel m1,m2;
JScrollPane scroll;

private String[] columnL ={"菜号","菜名","单价","数量","总计"};
private String[][] rowData = {{"1","套餐一","5", "0","0"},
        {"2","套餐二","4.5", "0","0"},
{"3","套餐三","7", "0","0"},
{"4","套餐四","9", "0","0"},
        {"5","套餐五","10", "0","0"}}; private JTable jTable;
        private JButton submit = new JButton("提交");
private JButton cencal = new JButton("取消");    @SuppressWarnings("empty-statement")
public orderform()
{
this.setTitle("电子点餐系统");//题目
                m1 = new JPanel();
                m2 = new JPanel();
                jTable = new JTable(rowData,columnL);
submit.addActionListener(this);
cencal.addActionListener(this);
//jTable.enable(false);
scroll = new JScrollPane();
                scroll.add(jTable);
                
                //scroll.setVisible(true);
                

               // m1.setVisible(true);
               // m1.setSize(900,400);
                m2.add(submit);
                m2.add(cencal);
                //m2.setSize(900,50);
                this.setLayout(new BorderLayout());
                add(BorderLayout.NORTH,scroll);
                add(BorderLayout.SOUTH,m2);
                this.add(m1);
this.setLocation(250, 140); //设置窗口的起始位置
        this.setSize(900, 450);
        this.setVisible(true);
} public void actionPerformed(ActionEvent e)
{
if( e.getSource() == submit)
{
Double sumtemp = 0.0;
for( int i = 0; i < 5; i++)
{
rowData[i][3] = jTable.getValueAt(i, 3).toString();
Double temp1 = Double.parseDouble(rowData[i][3]);
Double temp2 = Double.parseDouble(rowData[i][2]);
temp1 = temp1*temp2;
sumtemp += temp1;
rowData[i][4] = temp1.toString();/**/
//rowData[i][4]= jTable.getValueAt(i, 3).toString();
}
jTable.updateUI();
JOptionPane.showMessageDialog(this,
            sumtemp.toString()+"元", "总计",
            JOptionPane.INFORMATION_MESSAGE);
}
else if( e.getSource() == cencal )
{
                    new menu_next();
                    setVisible(false); }
} public static void main(String[] args)
{
orderform a = new orderform();
a.setVisible(true);
}
}

Answer 1

  scroll.add(jTable);
=> 
scroll.setViewportView(jTable);

Answer 2

        scroll = new JScrollPane(jTable);
    
        //scroll.setVisible(true);
            // m1.setVisible(true);
        // m1.setSize(900,400);
        m2.add(submit);
        m2.add(cencal);
        //m2.setSize(900,50);
        this.setLayout(new BorderLayout()); 
        add(scroll,BorderLayout.NORTH); // 参数次序颠倒
        add(m2,BorderLayout.SOUTH); // 参数次序颠倒
        this.add(m1); // 在中间加个空白的JPanel干什么 this多余的
        this.setLocation(250, 140); //设置窗口的起始位置
        this.setSize(900, 500); // 450 太小了 或者使用下面这行
        //pack(); 
        this.setVisible(true);