Sorting custom class array-list string using Collections.sort

Question

I am trying to sort my custom class array-list using Collections.sort by declaring my own anonymous comparator. But the sort is not working as expected.

My code is

Collections.sort(arrlstContacts, new Comparator<Contacts>() {

        public int compare(Contacts lhs, Contacts rhs) {

            int result = lhs.Name.compareTo(rhs.Name);

            if(result > 0)
            {
                return 1;

            }
            else if (result < 0)
            {
                return -1;
            }
            else
            {
                return 0;
            }
        }
    });

The result is not in sorted order.

Solution 1

Like Adam says, simply do:

Collections.sort(
  arrlstContacts, 
  new Comparator<Contacts>() 
  {
    public int compare(Contacts lhs, Contacts rhs) 
    {
      return lhs.Name.compareTo(rhs.Name);
    }
  }
);

The method String.compareTo performs a lexicographical comparison which your original code is negating. For example the strings number1 and number123 when compared would produce -2 and 2 respectively.

By simply returning 1, 0 or -1 there's a chance (as is happening for you) that the merge part of the merge sort used Collections.sort method is unable to differentiate sufficiently between the strings in the list resulting in a list that isn't alphabetically sorted.

Solution 2

As indicated by Adam, you can use return (lhs.Name.compareTo(rhs.Name)); likeso:

Collections.sort(arrlstContacts, new Comparator<Contacts>() {
     public int compare(Contacts lhs, Contacts rhs) {
         return (lhs.Name.compareTo(rhs.Name));
     }
});

Comments

[Paul Bellora]

Might want to cite Adam's comment.

[Mark Pazon]

Didn't see that it has been answered already in the comments. Editing... Thanks!