No valid constructor during serialization

Question

I have a major problem during loading the extension into the program. I get an exception as there is no valid constructor.

The problem is in the line:

Answer 1

The class Dydaktyk should have an accessible (public or protected) no-args constructor so that the serialization reflection mechanism can create an instance of the class:

public Dydaktyk() { 
  ...
}

From the docs

During deserialization, the fields of non-serializable classes will be initialized using the public or protected no-arg constructor of the class. A no-arg constructor must be accessible to the subclass that is serializable. The fields of serializable subclasses will be restored from the stream.