((DefaultTableModel) jTable2.getModel()).insertRow(countRows, new Object[]{ "1", "2", "3", "4" });

------解决方案--------------------

Java code

int countRows = jTable2.getRowCount();();//获取当前表格总行数
 int[] selectRows = jTable2.getSelectedRows                      int selectRow=jTable2.getSelectedRow();//选中的行数
if (selectRows.length == 0) {
((DefaultTableModel) jTable2.getModel()).insertRow(countRows, new Object[] { "1", "2", "3", "4" });
} else {
((DefaultTableModel) jTable2.getModel()).insertRow(selectRow + 1, new Object[] { "1", "2", "3", "4" });
                }