What's the difference between a not-initialed object and a null object

Question

hi guys, i wanna know the difference between a not-initialed object and a null object.
for eg.
Car c1;
Car c2 = null;after the 2 lines , 2 Car obj-referance have been created, but no Car obj.
1.so c2 is not refering to any object, so where do we put the null?in the heap?
2.as no c2 is not refering to any object, what's the difference between c2 and c1?
3.and where we store the difference-information?in the heap?

Answer 1

For local variables you can't have "Car c1;" the compiler will complain.That's not true. It will only complain if you try to use it without initializing it.
You can have (never used, so compiler doesn't care):
public void doSomething()
   Car c1;
   System.out.println("Hello");
}or you can have (definitely initialized, so doesn't have to be initialized where declared):
public void doSomething(boolean goldClubMember)
   Car c1;
   if (goldClubMember)
       c1 = new Car("Lexus");
   else
       c1 = new Car("Kia");
   System.out.println("You can rent a " + c1.getMake());
}