I need an anwer to this java program problem. Can anyone help me figure out how to solve it?

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The below program works fine for my first csv file but has an issue with my second csv file ( two individual csv files from two different tables). I tried using an arraylist but get the same problem. Basically it posts from a derby database correctly until it completes the 25th entry. Then it repeats again the last 3 entries posted to the csv file (23, 24, 25 ) and then continues posting the rest of the database entries correctly. However, I now have the posted entry row with the last entries no longer under the correct column heading and have 44 entries into the row instead of 41.
The database has 41 fields and the csv file is supposed to have one row with only 41 entries (columns). The method posts the header row correctly for all 41 columns. I really need to know how to resolve this. Any insight you provide would be helpful.

What I have tried:

The program actually work great on my other projects and outputs from derby to csv. It's just this one program seems to get stuck at the 25th database entry to the csv file. See below for the actual program:

private void saveCSV2() throws SQLException, IOException{
     	     doFieldsALL();//Method for setting the sqlquote2B headers in the CSV File
    	     String fileHeader = sqlquote2B; //Actual Header list
     	     String date;
     
    	    Date dt = new Date();
    	    SimpleDateFormat df = new SimpleDateFormat( "ddMMyyyy");
    	    date = df.format(dt);
     
    	     filename2 = filename ;//Gets the file path and name from the previous csv file method 
       	     Statement stmt;
        	     ResultSet rst;
       	     Connection b;
        		try {   
                   
           		 b = DriverManager.getConnection("jdbc:derby:plumberprodb"); //this is the derby database
                             String SQLD = "select * from PROJECTCOSTS"; //* this is the table in the database.             
                             stmt = b.createStatement();
                             rst = stmt.executeQuery(SQLD);

                             try (FileWriter fw = new FileWriter(filename + "2 -"+ date +".csv")) {
                                    fw.append(fileHeader);
                                    Writer append = fw.append(NEW_LINE_SEPARATOR);
                                   Writer fileWriter = new FileWriter(filename, false); //overwrites file

                                  while (rst.next()){
                                             ResultSetMetaData rsmd = rst.getMetaData();
                                             int columnCount = rsmd.getColumnCount();
                                           for(int i=1; i <=columnCount; i++) {
                                                          if(rst.getObject(i)!=null) {                               
                                                                 String data= rst.getObject(i).toString();
                                                                  if(rst.getObject(i) == null){
                                                                            data = " ";  } //accounst for empty fields
                                                                 fw.append(data) ;
                                                                 fw.append(",");  }                           
                                                      else {
                                                                String data= "null"; //accounts for null fields
                                                                fw.append(data) ;
                                                                fw.append(","); }
                                            }
                    		 //new line entered after each row
                     		fw.append(System.getProperty("line.separator"));
               		  }
                 		fw.flush();
             			}
                     
               	 } catch (SQLException e) {
              	         } catch (IOException ex) {
         		 Logger.getLogger(PlumberPROMAIN.class.getName()).log(Level.SEVERE, null, ex);
     		 }

  	  }

Posted 7-May-21 12:13pm

Bill Melendez

Updated 8-May-21 11:44am

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Richard MacCutchan 8-May-21 4:21am

What error and where does it occur?

2 solutions

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OriginalGriff · Answer 1 · 2021-05-07T19:50:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

But we can't help you directly - we don't have access to your data, and it's likely that that will be important to the problem.

Bill Melendez · Answer 2 · 2021-05-08T11:44:00

Solution 2

Problem solved. The issue was the derby db was not working correctly. Deleted it and redid the derby db. Works fine now. The above code is fine also.