What JAXB needs a public no-arg constructor for?

Question

What does JAXB need a public no-arg constructor for, during marshalling?

 Marshaller msh = ctx.createMarshaller();
 msh.marshal(object, System.out);
         


        

Answer 1

The same as many frameworks - simplicity and consistency. It allows the library to simple call Class.newInstance() without having to worry about how to specify certain dependencies for a constructor that takes them. JAXB doesn't want to concern itself with full-on Dependency Injection above and beyond the attribute-based setting it already does.

It's a shame in some ways as it means these classes can't be immutable, but that's the trade-off to be made.