如何在Java中执行Scala的Seq ++操作数

Question

I'm working with Scala's Seq class in Java ( scala.collection.Seq<A> ) and according to Scala documentation , there a ++ operand that merges two Seq into one. How can I do the same in Java?

Answer 1

Scala identifier ++ is translated into $plus$plus on JVM. Unfortunately, you can't call seq1.$plus$plus(seq2) , because the real signature of ++ is

def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That

and supplying the CanBuildFrom argument from Java is... technically possible, but not something you want to do.

So I suggest converting Scala collections to Java using JavaConverters methods before working with them in Java whenever CanBuildFrom gets involved.

Answer 2

To do the same in java, you could use the addAll method. Lets say you have two lists listOne and listTwo.

List<T> resultList = new ArrayList<T>(listOne);
resultList.addAll(listTwo);