JAVA EE: Java : Collection Framework : TreeSet (Arrange the names in descending order using Comparator)

Wednesday, 14 January 2015

Java : Collection Framework : TreeSet (Arrange the names in descending order using Comparator)

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DescendingNameComparator.java

import java.util.Comparator;

public class DescendingNameComparator implements Comparator<String>
{

    /*
     * This method used to arrange the names in descending order.
     */
    @Override
    public int compare( String name1, String name2 )
    {

        System.out
                .print("Compare method has been called in DescendingNameComparator, to arrange"
                        + " the names in decending order : ");

        System.out
                .println("name1 = " + name1 + ", name2 = " + name2 + "\n");

        return name2.compareTo(name1);
    }

}

TreeSetExample.java

import java.util.TreeSet;

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

        DescendingNameComparator decendingNameComparator = new DescendingNameComparator();

        /*
         * 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.
         */

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

        System.out.println("Balu" + " is going to be add in treeSet");
        treeSet.add("Balu");
        System.out.println("Ajay" + " is going to be add in treeSet");
        treeSet.add("Ajay");
        System.out.println("David" + " is going to be add in treeSet");
        treeSet.add("David");
        System.out.println("Charles" + " is going to be add in treeSet");
        treeSet.add("Charles");

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

    }
}

Output

Balu is going to be add in treeSet
Compare method has been called in DescendingNameComparator, to arrange the names in decending order : name1 = Balu, name2 = Balu

Ajay is going to be add in treeSet
Compare method has been called in DescendingNameComparator, to arrange the names in decending order : name1 = Ajay, name2 = Balu

David is going to be add in treeSet
Compare method has been called in DescendingNameComparator, to arrange the names in decending order : name1 = David, name2 = Balu

Charles is going to be add in treeSet
Compare method has been called in DescendingNameComparator, to arrange the names in decending order : name1 = Charles, name2 = Balu

Compare method has been called in DescendingNameComparator, to arrange the names in decending order : name1 = Charles, name2 = David

treeSet : [David, Charles, Balu, Ajay]