How TreeSet checks for Duplicates

Question

I am checking how TreeSet checks for duplicate elements and have the following code

  import java.util.*;

  public class TreeDemo{

    public static void main(         


        

Answer 1

TreeSet implements a balanced binary search tree based upon ordering of its members (via the Comparable or Comparator interfaces), not on hashing.

http://en.wikipedia.org/wiki/Self-balancing_binary_search_tree

Answer 2

a comparator return < 0, 0 or > 0... So equals is implemented by compareTo returning 0. Thus

if (node1.compareTo(node2) == 0) 

then the node is already in the set

Answer 3

TreeSet (or technically, the TreeMap that backs it) only uses the compareTo() function to compare the elements. It does not use Object's .equals() or .hashCode(). Moreover, if it had used any of them, your output would have been

[song1, song2, song3, song3]

because Object's default implementation uses memory addresses to test object equality, not their members.