Thread: Error: java.util.ConcurrentModificationException

Yesterday I hoped I had finished program 1, but it appears to have a fault in it.
And that is that it won't take empty cells.
(It is a program that read in an excel file to a MultiHashMap, uses Apache POI)
So know I have made this:

	public void OpenReadFileTwo() {
		// Open JFileChooser. 
		chooser2.showOpenDialog(null); 
		// Get the selected file. 
		java.io.File file2 = chooser2.getSelectedFile();
		// Create a FileInputStream. 
		FileInputStream fileInput2 = null; 
		//Get the name of the selected file. 
		fileName2= file2.getName();
		// Create a FileInputStream that will be used to read excel files. 
		try {
			fileInput2 = new FileInputStream(file2);
			// Create an excel workbook. 
			XSSFWorkbook workbook = new XSSFWorkbook(fileInput2); 
			// Get the first sheet. 
			XSSFSheet fileSheet2 = workbook.getSheetAt(0);
			// Create Iterator. 
			Iterator<Row> rows2 = fileSheet2.rowIterator();
 
			while (rows2.hasNext()) {
				//XSSF = .xlsx files, HSSF = .xls files. 
				XSSFRow row = (XSSFRow) rows2.next();
				// Get the empty cells in between as blank. 
				//row.getCell(blank, Row.CREATE_NULL_AS_BLANK);
				//System.out.println("Blank: " + row.getCell(blank, Row.CREATE_NULL_AS_BLANK));
 
				// Iterate the row. 
				Iterator<Cell> cells2 = row.cellIterator();
				// Count every time +1. 
				counterFile2 = counterFile2 +1; 
				//Get only the first column in the excel file, column A. 
				columnNumbers2 = "A" +counterFile2; 
				CellReference cellReference2 = new CellReference(columnNumbers2);
				Cell cellDataFirstColumn2 = row.getCell(cellReference2.getCol()); 
				// Change cellDataFirstColumn2 to a String format. 
				cellDataFirstColumn2String = "" + cellDataFirstColumn2; 
				// Store the first column data in an arrayList. 
				ArrayListFileData2.add(cellDataFirstColumn2String);
 
				while (cells2.hasNext()) {
					//
					XSSFCell cell2 = (XSSFCell) cells2.next();
					//
					row.getCell(blank, Row.CREATE_NULL_AS_BLANK);
					//System.out.println("Blank?: " + row.getCell(blank, Row.CREATE_NULL_AS_BLANK));
					String BlankOrNot = ("" + row.getCell(blank, Row.CREATE_NULL_AS_BLANK));; 
					//
					if (BlankOrNot.length() != 0) {
						System.out.println("Fish");
						//continue;
						Object cell2Object = "" + cell2;
						//
						mapFile2.put(cellDataFirstColumn2String, cell2Object);
						System.out.println("cell2Object: " + cell2Object);
					}
					else {
						System.out.println("Salmon");
						//
						Object blankeCell = " "; 
						mapFile2.put(cellDataFirstColumn2String, blankeCell);
						System.out.println("cell2Object: " + blankeCell);
					}
 
					blank = blank +1; 					
					System.out.println(blank);
 
 
				}
				blank = 0; 
			} counterFile2++; 
		} catch (IOException e2) {
			JOptionPane.showMessageDialog(null, "No file 2 selected, or the file is not a .xlsx file!");
		} finally {
			// Show the user the name of the selected file that was loaded in.
			label2.setText(" File selected: " + fileName2); 
			label2.setForeground(Color.BLUE);
		}
	}

And it looks like it is working, because it now grabs the empty cell and prints " " on my screen.
But after an empty cell have been found he runs to the catch.
And I looked up this error, and it says something is in use that I am not allowed to change.
But I don't see what is in use....

Also it only runs to the catch when an empty cell is found.
So if goes well, but else not.

And I don't understand why. -_-

That is a bit of the problem.
It only runs this subclass.
So it is not used somewhere else yet.

I think it is this one:
(When I remove this one I don't get the error.)

String BlankOrNot = ("" + row.getCell(blank, Row.CREATE_NULL_AS_BLANK));

But that is some code I need to find empty cells in between.

I found that code here:
java - How to get an Excel Blank Cell Value in Apache POI? - Stack Overflow

And I think that was the right way to implement it in my code.
Did I maybe made a mistake here?

There is not so much to be found on this function.
It only should make sure that empty cells are not skipped over.
And nothing else.

Originally Posted by Purple01

Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException

I would suggest you utilize your favorite search engine on java.util.ConcurrentModificationException so you understand what is going on.
Then if you have questions please post your code with the question. Just a little fyi, it is much easier to follow if you past more code that shows what you are trying to do rather than a bunch of snippets and comments about them.

Good luck with the exception, once you understand the exception you may be able to fix the cause of the problem.

I solved it.
I have put that line of code a few lines above and I made the line Return something.
Now it does work.

Thanks everyone.