Scala has a special syntax for invoking methods of arity-1 (one argument):
This syntax is formally known as “infix notation”. It should only be used for purely-functional methods (methods with no side-effects) - such as mkString -or methods which take functions as parameters - such as foreach:
names.mkString(",") // is the same as names mkString ","
Read more: Scala documentation: Method Invocation
// right! names foreach (n => println(n)) names mkString "," optStr getOrElse "
" // wrong! javaList add item