List to TreeSet conversion produces: “java.lang.ClassCastException: MyClass cannot be cast to java.lang.Comparable”

Question

List myclassList = (List) rs.get();

TreeSet myclassSet = new TreeSet(myclassList);

I d

Answer 1

If you don't pass an explicit Comparator to a TreeSet, it will try to compare the objects (by assuming they are Comparable). And if they aren't Comparable, it cannot compare them, so this exception is thrown!
TreeSets are sorted sets and require either objects to be Comparable or a Comparator to be passed in to determine how to sort the objects in the Set.