Question

I have a csv file with unknown amount of columns and row. The only thing I know is that each entry is separated by a comma. Can I use the split method to convert each line of the data into an array and then can I store that Array into an Arraylist. One of the things that concerns me is would I be able to rearrange the Arraylist alphabetically or numerically.

Answer 1

There are several questions here so I’ll cover each point individually.

Can I use the split method convert each line of the data into an array

This would work as you expect in the naive case. However, it doesn’t know anything about escaping; so if a comma is embedded within a field (and properly escaped, usually by double-quoting the whole field) the simple split won’t do the job here and will chop the field in two.

If you know you’ll never have to deal with embedded commas, then calling line.split(",") is acceptable. The real solution however is to write a slightly more involved parse method which keeps track of quotes, and possibly backslash escapes etc.

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…into an array than can I store that Array into an Arraylist

You certainly could have an ArrayList<String[]>, but that doesn’t strike me as particularly useful. A better approach would be to write a simple class for whatever it is the CSV lines are representing, and then create instances of that class when you’re parsing each line. Something like this perhaps:

public class Order {
    private final int orderId;
    private final String productName;
    private final int quantity;
    private final BigDecimal price;

    // Plus constructor, getters etc.
}

private Order parseCsvLine(String line) {
   String[] fields = line.split(",");

   // TODO validation of input/error checking
   final int orderId = Integer.parseInt(fields[0]);
   final String productName = fields[1];
   final int quantity = Integer.parseInt(fields[2]);
   final BigDecimal price = new BigDecimal(fields[3]);

   return new Order(orderId, productName, quantity, price);
}

Then you’d have a list of Orders, which more accurately represents what you have in the file (and in memory) than a list of string-arrays.

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One of the things that concerns me is would I be able to rearrange the Arraylist according alphabetically or numerically?

Sure – the standard collections support a sort method, into which you can pass an instance of Comparator. This takes two instances of the object in the list, and decides which one comes before the other.

So following on from the above example, if you have a List<Order> you can pass in whatever comparator you want to sort it, for example:

final Comparator<Order> quantityAsc = new Comparator<Order>() {
   public int compare(Order o1, Order o2) {
      return o2.quantity - o1.quantity; // smaller order comes before bigger one
   }
}

final Comparator<Order> productDesc = new Comparator<Order>() {
   public int compare(Order o1, Order o2) {
      if (o2.productName == null) {
         return o1.productName == null ? 0 : -1;
      }
      return o2.productName.compareTo(o1.productName);
   }
}

final List<Order> orders = ...; // populated by parsing the CSV

final List<Order> ordersByQuantity = Collections.sort(orders, quantityAsc);
final List<Order> ordersByProductZToA = Collections.sort(orders, productDesc);