我尝试使用JDBC使用PreparedStatement通过以下方法插入userId（int）和userName（String）：

public boolean saveUser(int userId, String userName){
    boolean saveStatus = false;
    try {
        connection.setAutoCommit(true);
        String sql = "insert into testtable values(?,?)";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1, userId);
        statement.setString(2, userName);
        saveStatus  = statement.execute(sql);
    } catch (SQLException e) {
        e.printStackTrace();
    }finally{
        Connector.closeConnections();
    }
    return saveStatus;
}

我得到以下堆栈跟踪：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in 
  your SQL syntax; check the manual that corresponds to your MySQL server version 
  for the right syntax to use near '?,?)' at line 1

我究竟做错了什么？