Question

I use scala.collection.immutable.HashMap<A,B> from some Java code and would like to use the Scala-native method toArray() to convert the contents (or values) of the map to an array.

I currently use JavaConversions.asMap() etc, and then use the traditional, but ugly, Java toArray(T[]) methods but I would prefer to call the Scala built in method directly instead.

This must be done from Java. Rewriting the code in Scala is not an option.

I am using Scala 2.9.1.

Answer 1

You need to supply a ClassManifest for the array type, T. This is available from the companion object (see note) for ClassManifest. So:

itr.toArray(ClassManifest$.MODULE$.fromClass(T.class));

In this example, T is a real type (not a type parameter). So for example, if itr were a Seq[String], you would use this;

itr.toArray(ClassManifest$.MODULE$.fromClass(String.class));

Because scala’s Map is actually a bunch of tuples, you would use this:

map.toArray(ClassManifest$.MODULE$.fromClass(Tuple2.class));

Of course, this gives you a Tuple2[], rather than a Tuple2<K,V>[] for the key and values types K and V respectively. As you are in Java-land, you can cast the raw type

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Note: accessing the companion object from Java.

The companion object of a type M is available by accessing the static field M$.MODULE$