NOT NULL Example :
"not null" means that the refernce is pointing to some object and stores "a memory address about how to get to the object in the memory"
Null Example :
a reference having a value null means that it doesn't point to any object.it is simply declaring a refernce variable
Getters and setters do not operate during the creation of the object, but by retrieval from the database or creation by instantiating the class;