Compare a converted TreeSet from a String with another TreeSet Java 7 - string

Question

Using Java 7 I am looking for a way to compare a string that I converted to a TreeSet with another defined TreeSet.
Here is an example:
public static <T> Set<T> intersection(Set<T> setA, Set<T> setB) {
Set<T> tmp = new TreeSet<T>();
for (T x : setA)
if (setB.contains(x))
tmp.add(x);
return tmp;
}
public static void main(String args[]) {
String str ="A, B, C, D";
Set<String> set3 = new TreeSet(Arrays.asList(str));
TreeSet<String> set1 = new TreeSet<String>();
TreeSet<String> set2 = new TreeSet<String>();
set1.add("A");
set1.add("B");
set1.add("C");
set1.add("D");
set2.add("A");
set2.add("B");
set2.add("C");
set2.add("D");
System.out.println("Intersection: Set 1 & 2: " + intersection(set1, set2));
System.out.println("Intersection: Set 1 & 3: " + intersection(set1, set3));
}
Comparing a set to another set that I used set.add to add its elments works as expected:
Intersection: Set 1 & 2: [A, B, C, D]
The issue that I can't get my head around is why I don't have a match when I compare a converted TreeSet from a String with another TreeSet.
Intersection: Set 1 & 3: []
But when I print set1 and set3 I find them to be exactly the same??
System.out.println("set1: " + set1);
System.out.println("set3: " + set3);
set1: [A, B, C, D]
set3: [A, B, C, D]
Then I tried looping through the string and added each element to the set but that didn't work either.
System.out.println("Intersection: (set1 - set3)" + intersection(set1, convertString2Set(str)));
private static Set convertString2Set(String line) {
List<String> linesList = new ArrayList<String>(Arrays.asList(line));
Set<String> set = new TreeSet<String>();
for (String elme : linesList) {
set.add(elme);
}
return set;
}

Answer 1

set3 in your code contains only one element: a string which is equal to "A, B, C, D". This string is not equal to either of four strings in set1, which are "A", "B', "C" and "D". The toString() representation of the two sets happens to be the same, but it does not mean that they have the same content.
Arrays.asList() on a String does not split anything; it will always create a single-element list. If you want to split a string into multiple substrings, use the String.split() method.