How to get inverse of a comparator in java

Question

In a method I receive a generic object E extends Comparable<E> as an argument. Now i want to create two priority queues.One which uses the comparator used by E and other queue which uses the opposite of comparator used by E(i.e. if E uses '<' then second queue must use '>='). Please hep me how to create two such queues.

queue2=new PriorityQueue<E>(0,Collections.reverseOrder(e));

I am getting the error that reverseOrder is not applicable.

please help

Answer 1

Look at Collections.reverseOrder.

Answer 2

Your object E extends java.lang.Comparable, but it is not a java.util.Comparator.

Create your first queue w/o a Comparator and you'll get the ordering in your compareTo function, then create a java.util.Comparator that does the comparison in reverse (just call a.compareTo(b) and then negate the result) and create your second queue with that comparator.