数据库查询时怎么检测结果集是否为空

try            {                con=DriverManager.getConnection("jdbc:MySQL://127.0.0.1:3306/Phone_Contacts", "root","fzg125009");                if(radio_name.isSelected())                {                    pre=con.prepareStatement("SELECT DISTINCT * FROM Contact WHERE name Like '"+field_name.getText()+"%'");                }                else if(radio_phone.isSelected())                {                    pre=con.prepareStatement("SELECT DISTINCT * FROM Contact WHERE mobile Like '"+field_phone.getText()+"%'");                }                rs=pre.executeQuery();                row=new CachedRowSetImpl();                row.populate(rs);                    if(row.wasNull())//这个不能被执行，所以这样检测不可以                {                    text.append("Sorry,无此记录!\n");                }                con.close();                while(row.next())                {                    text.append(row.getString(1)+"\t");                    text.append(row.getString(2)+"\n");                }            }            catch (SQLException error)            {                System.out.println("error!");            }