在JPanel上的JScrollpane中交换JTable

Question

今天我做了一些Web服务的实验。

一切都按预期工作。但现在我的gui有些问题。

我想向学生展示一个特定课程的表格。因此，我有一个组合框，包含所有可能的组和一个加载按钮。现在，我想在用户触发按钮后立即向学生展示所选课程。

我发现我的DAO对象工作正常，并且insertData方法使用正确的Vectors执行。不幸的是我的ScrollPane保持空白，没有显示任何表格。

每次选择新课程时，如何更改和显示表格？

package mycode.gui;

import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JLabel;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.util.List;
import java.util.Vector;

import javax.swing.SwingConstants;

import javax.swing.LayoutStyle.ComponentPlacement;
import javax.swing.JComboBox;
import javax.swing.JButton;
import javax.swing.JTable;

public class AbsenzenMelden extends JPanel {

    private JComboBox klassenwahl;
    private JButton laden;
    private JTable tabelle;
    private JScrollPane sp;

    public AbsenzenMelden() {

        JLabel headline = new JLabel("Bitte tragen Sie die Absenzen ein");
        headline.setHorizontalAlignment(SwingConstants.CENTER);
        headline.setFont(new Font("Tahoma", Font.PLAIN, 13));

        JLabel lblKlasse = new JLabel("Klasse:");
        lblKlasse.setFont(new Font("Tahoma", Font.PLAIN, 13));

        klassenwahl = new JComboBox();
        klassenwahl.setFont(new Font("Tahoma", Font.PLAIN, 13));

        laden = new JButton("laden");
        laden.setFont(new Font("Tahoma", Font.PLAIN, 13));

        tabelle = new JTable();
        sp = new JScrollPane(tabelle);



        JButton okbutton = new JButton("speichern");
        okbutton.setFont(new Font("Tahoma", Font.PLAIN, 13));
        GroupLayout groupLayout = new GroupLayout(this);
        groupLayout.setHorizontalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addContainerGap()
                    .addGroup(groupLayout.createParallelGroup(Alignment.LEADING)
                        .addComponent(sp, GroupLayout.DEFAULT_SIZE, 430, Short.MAX_VALUE)
                        .addComponent(headline, GroupLayout.DEFAULT_SIZE, 430, Short.MAX_VALUE)
                        .addGroup(groupLayout.createSequentialGroup()
                            .addComponent(lblKlasse, GroupLayout.PREFERRED_SIZE, 75, GroupLayout.PREFERRED_SIZE)
                            .addGap(18)
                            .addComponent(klassenwahl, GroupLayout.PREFERRED_SIZE, 206, GroupLayout.PREFERRED_SIZE)
                            .addGap(31)
                            .addComponent(laden))
                        .addComponent(okbutton, Alignment.TRAILING))
                    .addContainerGap())
        );
        groupLayout.setVerticalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addContainerGap()
                    .addComponent(headline, GroupLayout.PREFERRED_SIZE, 37, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(ComponentPlacement.RELATED)
                    .addGroup(groupLayout.createParallelGroup(Alignment.BASELINE)
                        .addComponent(lblKlasse, GroupLayout.PREFERRED_SIZE, 25, GroupLayout.PREFERRED_SIZE)
                        .addComponent(klassenwahl, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                        .addComponent(laden))
                    .addGap(18)
                    .addComponent(sp, GroupLayout.DEFAULT_SIZE, 107, Short.MAX_VALUE)
                    .addGap(10)
                    .addComponent(okbutton, GroupLayout.PREFERRED_SIZE, 25, GroupLayout.PREFERRED_SIZE)
                    .addContainerGap())
        );
        setLayout(groupLayout);

    }

    public void insertKlassen(List<String>klassen)
    {
        for (String aktuell : klassen)
        {
            klassenwahl.addItem(aktuell);
        }
    }

    public String getKlasse()
    {
        return (String) klassenwahl.getSelectedItem();
    }

    public void addLadenListener(ActionListener al)
    {
        laden.addActionListener(al);
    }

    public void insertData(Vector data, Vector head)
    {
        tabelle = new JTable(data, head);
        tabelle.getColumn("id").setMinWidth(0);
        tabelle.getColumn("id").setMaxWidth(0);
        tabelle.repaint();
        tabelle.revalidate();
        sp.repaint();
        sp.revalidate();

    }
}