How to: enrich / contat scala immutable lists from Java

enrich_scala_lists_in_java.java

package test;

import scala.collection.mutable.ListBuffer;
import scala.collection.immutable.List;

public class Demo {
  public static void main(String[] args) {
    List immutable = new List();
    ListBuffer mutable = new ListBuffer();
    ListBuffer mutable2 = new ListBuffer();
    
    mutable.$plus$eq("1");
    mutable2.$plus$eq("2");
    mutable.$plus$plus$eq(mutable2);
    
    immutable = mutable.toList(); // [ "1", "2" ]
    
    mutable.$plus$plus$eq(immutable);
    
    immutable = mutable.toList(); // [ "1", "2", "1", "2" ]
  }
}