Question

I try to readout a csv-File. In my Code I readout the Lines in the csv-File. Therefor I use an arraylist to add each item in the line to the arraylist.

After reading out a line i storte the array list in an other array list and then go to read out the next line and so on and ao on.

Now I have here a few Questions and one Problem.

1) When I add an item to an arraylist is it always added at the en of the list (When I give no specific place where to add the item like in my code)? With this then the order of the csv-file would be keeped.

2) I figuered out, that when I clear the arraylist datatemp to prepare the reading of the next line, also the content of the array list data is cleared. How can I prevent my code from doing so?

3) Is there a way to make an normal array out of the arraylist data I have?

4) Is my way of reading out the csv-File correct or is there any better way?

public class CSVReader {    

public void ReadCSV (String csvfilepath) {

    BufferedReader CSVFile = null;
    String dataRow = null;
    ArrayList<Float> datatemp = new ArrayList<Float>(); 
    ArrayList<ArrayList<Float>> data = new ArrayList<ArrayList<Float>>(); 

    try {
        CSVFile = new BufferedReader(new FileReader(csvfilepath));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    try {
        dataRow = CSVFile.readLine();
    } catch (IOException e) {
        e.printStackTrace();
    }

    while (dataRow != null){
        String[] dataArray = dataRow.split(",");
        for (String item:dataArray) {
            datatemp.add(Float.valueOf(item));
        }
        try {
            dataRow = CSVFile.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }

        data.add(datatemp);
        datatemp.clear();
    }

    try {
        CSVFile.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
    }
} 

Answer 1

1) With this then the order of the csv-file would be keeped.

Yes

2) How can I prevent my code from doing so?

You need to create a new tempArrayList each time:

while (dataRow != null){
    datatemp = new ArrayList<Float>();

3) Is there a way to make an normal array out of the arraylist data I have?

You can create an array of arraylists:

ArrayList[] array = data.toArray(new  ArrayList[data.size()]);

You can do then it recursively to create a 2D array, but I would stick to the list of list which is easier to handle.

4) Is my way of reading out the csv-File correct or is there any better way?

Use a library, there are many of them, which has been tested. It is much more difficult to parse a CSV file correctly than it seems at first sight.