Code that does not allow opening an Internalframe twice

Sorry if you do not specify the question correctly. The code you insert in the page allows you to not open a window Interframe twice. I do not understand some lines of code, such as

private void cargarFormInterno(Class<?> aClass)

I do not know why they used the parameters ClassClass<?> aClass of the private.

For this reason I request the explanation of the code.