See the user description: http://mail.openjdk.java.net/pipermail/macosx-port-dev/2013-June/005770.html

Hi,

I noticed that on Java 8 on Mac, the JTableHeader looks clipped (the bottom line is not visible).
This was not an issue in Java 6.

Here is a simple test case:

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;

public class JTableHeaderTest
{
public void run()
{
JTable table = new JTable(2, 5);

JScrollPane scrollableTable = new JScrollPane(table);

JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(scrollableTable);
frame.setSize(300, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}

public static void main(String[] arguments)
{
SwingUtilities.invokeLater(new Runnable()
{
@Override
public void run()
{
JTableHeaderTest test = new JTableHeaderTest();
test.run();
}
});
}
}