【发布时间】：2013-07-13 02:27:59
【问题描述】：
我有应该查询 Derby 数据库的代码，但没有。更糟糕的是，它应该在不同的行打印错误消息，但甚至无法做到这一点。这是我的代码的 sn-p（我遇到问题的地方）：
try
{
connection = DriverManager.getConnection(DATABASE_URL);
//setting up the statement to handle our initial query
statement = connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
resultSet = statement.executeQuery("SELECT TripNumber,AverageSpeed FROM " +
"BikeTripRecords WHERE TripNumber=(SELECT count(TripNumber) FROM " +
"BikeTripRecords)");
//initializing maxShowableRecords depending on the number of BikeTrips already
//recorded to the database
if (!resultSet.next())
{
System.err.println("There was a problem processing your query.");
System.out.println("This error occurred on line 86");
}
else
{
tripCount = resultSet.getInt(1);
this.maxShowableRecords = (((x < tripCount) && (x > 1)) ? x :
tripCount);
lastTripSpeed = resultSet.getDouble(2);
}
//getting information about their trip history (and their last trip)
resultSet = statement.executeQuery("SELECT * FROM BikeTripAnalysis");
System.out.println("This error occurred on line 98");
if (!resultSet.next())
{
System.err.println("There was a problem processing your query.");
}
else
{
//storing the values in the view to variables so that we don't have to keep
//querying the database
minSpeed = resultSet.getDouble(1);
maxSpeed = resultSet.getDouble(2);
avgSpeed = resultSet.getDouble(3);
resultSet.close();
//forming the statement to display
messageToDisplay = String.format("Out of the %d trips you have " +
"recorded, these are your stats:\n\nMinimum Speed == " +
"%f\nMaximum Speed == %f\nAverage Speed == %.2f\n\nYour Last " +
"Speed == %.2f", tripCount, minSpeed, maxSpeed, avgSpeed,
lastTripSpeed);
if ((lastTripSpeed == minSpeed) && (tripCount > 1))
{
messageToDisplay += "Your last average speed was your worst. You " +
"can do better!!";
}
else
{
if ((lastTripSpeed == maxSpeed) && (tripCount > 1))
{
messageToDisplay += "\n\nYou have set a new speed record!! " +
"Keep on keeping on!!";
}
else
{
if (lastTripSpeed < avgSpeed)
{
messageToDisplay += "\n\nYou are below your average. Step" +
" it up!";
}
else
{
messageToDisplay += "\n\nYou are above your average. Keep." +
" It. Up!!";
}
}
//showing the user this message
JOptionPane.showMessageDialog(this, messageToDisplay);
}
}
}
catch (SQLException exception)
{
exception.printStackTrace();
System.exit(1);
}
雪上加霜的是，MessageDialog 在不应该显示的时候显示。
事实上，我得到的是这样的：
There was a problem processing your query.This error occurred on line 86
This error occurred on line 98
【问题讨论】：
-
OK ... 那么它实际输出的是什么？
-
我知道我应该只依赖 Java 默认提供的面向对象的数据库。
-
迈克——如果你需要帮助，你需要回答我的问题。否则，我们只是在这里浪费时间。 StackExchange 不是发布有关 Java 的投诉的合适场所...
-
（并且Java默认不提供任何数据库。它们都是3rd-party产品......关于Java SE，EE，ME......）
-
是的，确实如此。它提供对象序列化，将对象序列化为字节形式以存储在文件（数据库）中。