Auto conversion between scala and java collections when using scala.collection.JavaConversions._ in scala 2.8

Question

I have java API which return this type:

ArrayList[ArrayList[String]] = Foo.someJavaMethod()

In scala program, I need to send above type as a parameter to a scala function 'bar' whose type is

def bar(param: List[List[String]]) : List[String] = {

}

so I call bar like:

val list = bar(Foo.someJavaMethod())

but this does not work as I get compile error.

I thought have this import

import scala.collection.JavaConversions._

will do implicit automatic conversion between Java and Scala collections.

I also tried using like:

Foo.someJavaMethod().toList

but that does not work either.

What is the solution to this problem?

Jean-Philippe Pellet · Accepted Answer · 2011-07-07 12:00:20Z

7

First, ArrayList does not convert to List, it converts to a Scala Buffer. Second, implicit conversion will not recurse into the elements of your collections.

You'll have to manually map the inner lists. Either with implicit conversions:

import collection.JavaConversions._
val f = Foo.someJavaMethod()
bar(f.toList.map(_.toList))

Or, more explicitly, if you prefer:

import collection.JavaConverters._
val f = Foo.someJavaMethod()
bar(f.asScala.toList.map(_.asScala.toList))

answered Jul 7, 2011 at 12:00

Jean-Philippe Pellet

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