Swing: can't seem to get JTable to show properly

The following code shows a bug I'm trying to fix. I have two ways of 开发者_如何学运维displaying a table (hierarchy below):

1. JTable directly in a JOptionPane: shows the table fine.

   JOptionPane
       JTable
   

2. JTable in a scrollpane in a JPanel in a JOptionPane: can't seem to show the table.

   JOptionPane
       JPanel
           JScrollPane
               JTable
   

Since it's the same function to create the table, I'm fairly positive that I'm just doing something wrong w/r/t sizing/layout. Any suggestions?

import java.awt.Dimension;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;

public class TableTest2 {   
    public static void testTable(JTable t) {
        t.setModel(new AbstractTableModel() {
            public String getColumnName(int col) { return "col"+Integer.toString(col); }
            public int getRowCount() { return 4; }
            public int getColumnCount() { return 4; }
            public Object getValueAt(int row, int col) {
                return Integer.toString(row*col);
            }
            public boolean isCellEditable(int row, int col) { return false; }
            public void setValueAt(Object value, int row, int col) { }
        });
    }
    public static void main(String[] args) {
        doTest1();
        doTest2(null, null);
        doTest2(new Dimension(500,500), null);
        doTest2(new Dimension(500,500), new Dimension(400,400));
    }
    private static void doTest1() {
        JTable t = new JTable();
        t.setPreferredSize(new Dimension(500,500));
        TableTest2.testTable(t);
        JOptionPane.showMessageDialog(null, t, "test1", JOptionPane.INFORMATION_MESSAGE);
    }
    private static void doTest2(Dimension d1, Dimension d2) {
        JTable t = new JTable();
        TableTest2.testTable(t);
        JPanel panel = new JPanel();
        JScrollPane sp = new JScrollPane();
        sp.add(t);
        if (d1 != null)
            sp.setPreferredSize(d1);
        panel.add(sp);
        if (d2 != null)
            panel.setPreferredSize(d2);
        JOptionPane.showMessageDialog(null, panel, "test2", JOptionPane.INFORMATION_MESSAGE);
    }
}

Try this:

  JScrollPane sp = new JScrollPane(t);

providing the component for the scrollpane in the constructor.

You do not add components to the scrollpane. You can set a viewport lik ethis:

  sp.getViewPort().setView(t);

rather than

  sp.add(t);