How to instantiate a Transformer in JUNG2 with Scala and Ints as vertices?

Question

I am trying to create my own Transformer for shape and size of nodes in a visualization with JUNG2.

However, I keep running into typing problems. I narrowed down my problem to the following example.

PluggableRenderContext in JUNG does a simple instantiation of ConstantTransformer, where V is the vertex type:

protected Transformer<V,Shape> vertexShapeTransformer = 
    new ConstantTransformer(
    new Ellipse2D.Float(-10,-10,20,20));

However, if I do my own instantiation in Scala like so

val vertexShapeTransformer: Transformer[Int, Shape] =
  new ConstantTransformer(new Ellipse2D.Float(-10,-10,20,20));

I get a typing error:

type mismatch;
found: org.apache.commons.collections15.functors.ConstantTransformer[java.awt.geom.Ellipse2D.Float]
required: org.apache.commons.collections15.Transformer[Int,java.awt.Shape]"

As far as I understand, the types are conceptually compatible: ConstantTransformer is-a Transformer[Object, Shape] and Ellipse2D is-a Shape.

I assume it boils down to the fact that Scala's Int is not an Object. I cannot find a solution for this problem, though, but cannot imagine that this whole part of the library is rendered unusable as a result.

What can I do about it?

Answer 1

You might need to give scala a little help with the types. I'm not sure if this will work but you could try typing the ConstantTransformer:

  val vertexShapeTransformer: Transformer[Int, Shape] =
    new ConstantTransformer[Shape](new Ellipse2D.Float(-10,-10,20,20))

UPDATE

This should work, the type that you can pass to Transformer is anything up to Integer (not Int):

  val vertexShapeTransformer: Transformer[_ >: Integer, Shape] =
    new ConstantTransformer(new Ellipse2D.Float(-10,-10,20,20))