implement generic generic interface in scala

Question

From scala I need to create a java object than it has a method that it demands a parameter that it is a generic interface

java class

public class JavaTest<T> {
    public List<T> add(IJavaTest<T> javaTest){
        return null;
    }
}

java interface

public interface IJavaTest<T> {
    String ss();
}

and in scala I implement this:

val javaTest = new JavaTest

class TMijavatest[T] extends IJavaTest[T] {
  override def ss(): String = ""
}

val foo=new TMijavatest()

But when I call the add method

javaTest.add(foo);

I have this error in intellij: Type mismatch, expected:IJavaTest[T], actual TMijavatest[Nothing]

with:

javaTest.add(foo.asInstanceOf);

It compiles me but in execution time I have this error:

Unexpected error occured in the server. Caused by: java.lang.ClassCastException: my.pakage.Test$TMijavatest$1 cannot be cast to scala.runtime.Nothing$

if I generate the foo object just like this:

 val foo = new TMijavatest[String]
 javaTest.add(foo);

I have this error in intellij: Type mismatch, expected:IJavaTest[T], actual TMijavatest[String]

How I can do this? Thank you

Class TMijavatest takes a type parameter, but you are instantiating it without a type argument, so Nothing is inferred. Specify the type argument. For example: val foo = new TMijavatest[String]() — Jesper
– Jesper, Commented Aug 19, 2015 at 11:00
The same holds true for the JavaTest class. It is a generic type, thus you should instantiate it with a type, e.g. val javaTest = new JavaTest[String]. — Till Rohrmann
– Till Rohrmann, Commented Aug 19, 2015 at 11:46

aloon · Accepted Answer · 2015-08-19 12:16:09Z

1

You should instantiate JavaTest & TMijavatest with type

val javaTest = new JavaTest[String]

class TMijavatest[T] extends IJavaTest[T] {
  override def ss(): String = ""
}

val foo = new TMijavatest[String]

javaTest.add(foo)

answered Aug 19, 2015 at 12:16

aloon

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