code: public static IFunctionType getRepresentativeFunctionType( IType interfaceType )
    {
      IMethodInfo javaMethodInfo = getSingleMethod( interfaceType );
      if( javaMethodInfo != null )
      {
        return GosuShop.createFunctionType( javaMethodInfo );
      }
      else
      {
        return null;
      }
    }
docs: ## WARNING: call interfaceType.getFunctionalInterface() instead, it caches the result