clearly, the order of execution is
valueBound for the first one
valueBound for the second one (because the value of the first one will be unBound only after it is replaced)
valueUnbound for the first one
(here, the
string value is added, but the String class doesn't implement the HttpSessionBindingListener, so valueBound or Unbound won't be called for adding or removing "x")
valueUnbound for the second one (because it has now been replaced by "x")
so clearly, the outpu will be
B B UB UB
