Question

It should return true if one HashSet A is a subset of another HashSet B, false otherwise.

Answer 1

Not sure if it has to be a strict subset or it can be equal.

Set a = ...
Set b = ...

If you can use containsAll

return b.containsAll(a);

or if it has to be a strict subset

return b.size() > a.size() && b.containsAll(a);

or you can

Set tmp = new HashSet(a);
tmp.removeAll(b);
return tmp.isEmpty();