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我尝试使用JDBC使用以下方法使用PreparedStatement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stacktrace:

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？