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DescendingAlphabetsComparator.java

import java.util.Comparator;

public class DescendingAlphabetsComparator implements Comparator<String>
{

    /*
     * This method used to arrange the Alphabets in descending order.
     */
    @Override
    public int compare( String alphabet1, String alphabet2 )
    {

        System.out
                .print("Compare method has been called in DescendingAlphabetsComparator, to arrange"
                        + " the Alphabets in descending order : ");

        System.out
                .println("alphabet1 = " + alphabet1 + ", alphabet2 = " + alphabet2 + "\n");

        return alphabet2.compareTo(alphabet1);
    }

}

import java.util.TreeSet;

/*
 * Example of  TreeSet(Comparator<? super E> comparator) Constructor.
 */
public class TreeSetExample
{
    public static void main(String[] args)
    {

        /*
         * Constructs a new, empty tree set, sorted according to the specified
         * comparator.
         * 
         * All elements inserted into the set must be mutually comparable by the
         * specified comparator: comparator.compare(e1, e2) must not throw a
         * ClassCastException for any elements e1 and e2 in the set.
         * 
         * If the user attempts to add an element to the set that violates this
         * constraint, the add call will throw a ClassCastException.
         */
        DescendingAlphabetsComparator descendingAlphabetsComparator = new DescendingAlphabetsComparator();

        TreeSet<String> treeSet = new TreeSet<String>(
                descendingAlphabetsComparator);

        System.out.println("B" + " is going to be add in treeSet");
        treeSet.add("B");
        System.out.println("C" + " is going to be add in treeSet");
        treeSet.add("C");
        System.out.println("A" + " is going to be add in treeSet");
        treeSet.add("A");
        System.out.println("B" + " is going to be add in treeSet");
        treeSet.add("D");

        System.out.println("treeSet : " + treeSet + "\n");

    }
}