can StringBuffer objects be keys in TreeSet in Java?

Question

I have the following code where I am trying to put the StringBuffer objects as keys in a TreeSet. The reason I do this is to see if I can put mutable objects as keys. I do n

Answer 1

TreeSet takes only Comparable objects where as StringBuffer is not Comaprable object.

TreeSet#add

Throws-ClassCastException - if the specified object cannot be compared with the elements currently in this set.

You can use String object(Since String is Comparable) instead of StringBuffer object.
For example:

    Set sb=new TreeSet();
    sb.add(one.toString());
    sb.add(two.toString());
    sb.add(three.toString());
    System.out.println("set before change: "+ sb);
    System.out.println("set After change: "+ sb);