Why Custom user type requires a public default constructor ?

org.hibernate.type.CustomType instantiates the Custom User Type which required the default constructor of the custom user type to be public.

It should have been allowed to have private default constructor in the custom user type and that could have still be instantiated by the hibernate using the following code;

Constructor<?> constructor = MaintenanceType.class.getDeclaredConstructor(null);
constructor.setAccessible(true);
constructor.newInstance(null);


Please give your valuable Suggestions....