Java 2D ArrayList and sorting

Question

I need to sort a shopping list by the aisle the item is located for example:
[Bread] [1]
[Milk] [2]
[Cereal] [3]

I am planning to do this with ArrayList and was wondering how to make an 2D ArrayList Bonus questions: any ideas on how to sort by the aisle number?

Answer 1

Don't you have a class that holds your item + aisle information? Something like:

public class Item {
  private String name;
  private int aisle;

  // constructor + getters + setters 
}

If you don't, consider making one - it's definitely a better approach than trying to stick those attributes into ArrayList within another ArrayList. Once you do have said class, you'll either need to write a Comparator for your objects or make 'Item' Comparable by itself:

public class Item implements Comparable<Item> {
  .. same stuff as above...

  public int compareTo(Item other) {
    return this.getAisle() - other.getAisle();
  }
}

Then all you do is invoke sort:

List<Item> items = new ArrayList<Item>();
... populate the list ...
Collections.sort(items);

Answer 2

If you want to sort an ArrayList of ArrayLists then you can use the ColumnComparator.

If you want to sort an ArrayList of your custom Object then you can use the BeanComparator.