Concrete class of ClassWithAssitedInjectionFactory is auto generated by Guice. How it is looks like is explained in the Guice official page.

https://github.com/google/guice/wiki/AssistedInject#factories-by-hand

According to the page,

```

AssistedInject maps the create() method's parameters to the corresponding @Assisted parameters in the implementation class' constructor. For the other constructor arguments, it asks the regular Injector to provide values.

```