"" + set.size()new Integer(set.size()).toString()
The return type of the Set.size() method is int, but it is desired a conversion to String. These two lines do the conversion, but the first use the penalty of a concatenation operation ((new StringBuilder().append(i).toString())) and the second one creates an intermediate Integer wrapper. So, the right way to convert numbers to Strings is:
Integer.toString(set.size())