How do I initialize a Scala map with more than 4 initial elements in Java?
- by GlenPeterson
For 4 or fewer elements, something like this works (or at least compiles):
import scala.collection.immutable.Map;
Map<String,String> HAI_MAP = new Map4<>("Hello", "World",
"Happy", "Birthday",
"Merry", "XMas",
"Bye", "For Now");
For a 5th element I could do this:
Map<String,String> b = HAI_MAP.$plus(new Tuple2<>("Later", "Aligator"));
But I want to know how to initialize an immutable map with 5 or more elements and I'm flailing in Type-hell.
Partial Solution
I thought I'd figure this out quickly by compiling what I wanted in Scala, then decompiling the resultant class files. Here's the scala:
object JavaMapTest {
def main(args: Array[String]) = {
val HAI_MAP = Map(("Hello", "World"),
("Happy", "Birthday"),
("Merry", "XMas"),
("Bye", "For Now"),
("Later", "Aligator"))
println("My map is: " + HAI_MAP)
}
}
But the decompiler gave me something that has two periods in a row and thus won't compile (I don't think this is valid Java):
scala.collection.immutable.Map HAI_MAP =
(scala.collection.immutable.Map)
scala.Predef..MODULE$.Map().apply(scala.Predef..MODULE$.wrapRefArray(
scala.Predef.wrapRefArray(
(Object[])new Tuple2[] {
new Tuple2("Hello", "World"),
new Tuple2("Happy", "Birthday"),
new Tuple2("Merry", "XMas"),
new Tuple2("Bye", "For Now"),
new Tuple2("Later", "Aligator") }));
I'm really baffled by the two periods in this:
scala.Predef..MODULE$
I asked about it on #java on Freenode and they said the .. looked like a decompiler bug. It doesn't seem to want to compile, so I think they are probably right. I'm running into it when I try to browse interfaces in IntelliJ and am just generally lost.
Based on my experimentation, the following is valid:
Tuple2[] x = new Tuple2[] { new Tuple2<String,String>("Hello", "World"),
new Tuple2<String,String>("Happy", "Birthday"),
new Tuple2<String,String>("Merry", "XMas"),
new Tuple2<String,String>("Bye", "For Now"),
new Tuple2<String,String>("Later", "Aligator") };
scala.collection.mutable.WrappedArray<Tuple2> y = scala.Predef.wrapRefArray(x);
There is even a WrappedArray.toMap() method but the types of the signature are complicated and I'm running into the double-period problem there too when I try to research the interfaces from Java.
