Question

I need to implement the following function. I’m open to using the best class, but I’m not sure whether I should use SortedSet or TreeSet (as in Set myEmailsAscending = new TreeSet(new DateAscendingComparator()); // emails are always in ascending order).

public void addEmail(Email email)//The prototype isn't to be altered.
{
Comparator comp;
if(getCurrentSortingMethod()=="DateDescending") comp=DateDescendingComparator;
else if(getCurrentSortingMethod()=="DateAscending") comp=DateAscendingComparator;
...//other comparators

int index = Collections.binarySearch(getEmails(), email, new comp());// Search where to insert according to the current sorting method.
getEmails().add(-index-1, email);}// Add the item to the list
}

Is that the proper syntax to choose comparator?
I’d like to avoid creating multiple Comparator classes so is there a way to do this?

Answer 1

There are several issues:

You should use equals() for string comparison and not ==.

The usage of new is wrong. I’d suggest the following:

Comparator comp;
if (getCurrentSortingMethod().equals("DateDescending")) {
   comp = new DateDescendingComparator();
} else if (getCurrentSortingMethod().equals("DateAscending")) {
   comp = new DateAscendingComparator();
} ...

int index = Collections.binarySearch(getEmails(), email, comp);

Note how the new has been moved inside the if blocks.

As an alternative to all this, you could use a SortedSet<Email> with the appropriate comparator. The set will be automatically kept sorted in the correct order.