GridBagLayout: Multiple Rows (3)

   // two in one row
   c.gridwidth = 1;
   gridbag.setConstraints(btn4, c);
   c.gridwidth = GridBagConstraints.REMAINDER;
   gridbag.setConstraints(btn5, c);

   // row by itself
   c.gridwidth = GridBagConstraints.REMAINDER;
   gridbag.setConstraints(btn6, c);

   resize(600, 300);
   show();
}