Using Scala collections from Java

CollectionTest.java

package org.example;

import scala.Function1;
import scala.collection.generic.CanBuildFrom;
import scala.collection.immutable.List;
import scala.collection.immutable.List$;
import scala.collection.immutable.Vector;
import scala.collection.immutable.Vector$;
import scala.collection.mutable.Builder;
import scala.runtime.AbstractFunction1;

public class ScalaCollectionTest {
    
    // With proper setup, it doesn't seem too bad. 
    
    public static void main(String[] args) {        
        List<String> strings = list("one", "two", "three");
        System.out.println(strings.toString());
        strings.map(length, ListBuilder.<String, Integer>newCBF()).foreach(println);
        
        
        Vector<String> stringv = vector("four", "five", "six");
        System.out.println(stringv.toString());
        Vector<Integer> outv = stringv.map(length, VectorBuilder.<String, Integer>newCBF());
        outv.foreach(println);
    }

    /******************************************************/
    /*** Pay no attention to the man behind the curtain ***/
    /******************************************************/
    
    public final static Function1<String, Integer> length = new AbstractFunction1<String, Integer>() {

        @Override
        public Integer apply(String arg0) {
            return arg0.length();
        }
    };
    
    public final static Function1<Integer, Void> println = new AbstractFunction1<Integer, Void>() {
        @Override
        public Void apply(Integer arg0) {
            System.out.println(arg0);
            return null;
        } 
    };
    
    final static class VectorBuilder { 
        public static <Source, Target> CanBuildFrom<Vector<Source>, Target, Vector<Target>> newCBF() { 
            return new CanBuildFrom<Vector<Source>, Target, Vector<Target>>() {
                Vector<Target> v = Vector$.MODULE$.<Target>empty();
    
                @Override
                public Builder<Target, Vector<Target>> apply() {
                    return v.newBuilder();
                }
    
                @Override
                public Builder<Target, Vector<Target>> apply(Vector<Source> arg0) {
                    return v.newBuilder();
                }
            };
        }
    }
    
    final static class ListBuilder { 
        public static <Source, Target> CanBuildFrom<List<Source>, Target, List<Target>> newCBF() { 
            return new CanBuildFrom<List<Source>, Target, List<Target>>() {
                List<Target> v = List$.MODULE$.<Target>empty();
    
                @Override
                public Builder<Target, List<Target>> apply() {
                    return v.newBuilder();
                }
    
                @Override
                public Builder<Target, List<Target>> apply(List<Source> arg0) {
                    return v.newBuilder();
                }
            };
        }
    }
    
    public final static <A> List<A> list(A... as) {
        List<A> l = List$.MODULE$.empty();
        for (int i = as.length - 1; i >= 0; i--) { 
            l = l.$colon$colon(as[i]);
        }
        return l;
    }

    public final static <A> Vector<A> vector(A... as) { 
        Vector<A> v = Vector$.MODULE$.empty();
        for (A a : as) { 
            v = v.appendBack(a);
        }
        return v;
    }
}

output

List(one, two, three)
3
3
5
Vector(four, five, six)
4
4
3