But I am not able to get what is actual use of this in set ?
A comparator is something whose purpose is to compare two elements. It is passed to the sorted set, for cases where you want the sorted set to sort elements which are not comparable. Or if you want the elements sorted in a fashion that is different from the natural ordering provided by the comparable elements.
One part of the Java Tutorials you might do well to read is about Collections. Read it very quickly and you will forget 99% of what you read. No problem: you can always go back and read it again.
As you go through it, you will come across a section about object ordering. That tells you about Comparators.
