How to use a object created in a subclass of a abstract class, in the abstract class

Question

I have created a plane seat booking system via a brief that was provided by my university for a assignment. I am running into one main problem that I just can not figure out.

The brief states that the abstract class must have one abstract method and about 4 public methods. In both of the subclasses of the abstract class we have to initialize the array of objects (all plain seats). However, once they are initialized I do not know how I can send them back to the abstract class (which has a method that checks for unbooked plane seats, this is where I need the initialized seat object)

ArrayIndexOutOfBounds on a object that should be in bounds

The above link contains every single one of the classes and their code, I had a previous error which someone helped me fix and just thought it would be easier to link the full files here.

I just want to use the initialized array of objects (seats) created in a subclass of a abstract class, in the abstract class.

All input is greatly appreciated!

Is there a reason why PetiteFloorGrid has it's own `Seat[][] newSeats`, rather than directly using (including initialising) FloorGrid's `Seat[][] seat` (and so answering the question) ? — racraman, Sep 02 '19 at 00:22
ps, little tip : using `protected` is great, but that does also allow access from classes in the same package - eg, you are still allowing `TrainSeatBookingApplication` to have access to the variables. Better to keep everything `private`, or use protected together with judicious creation of packages for inheritance trees. — racraman, Sep 02 '19 at 00:27
You guys are awesome, thank you so much for all this information! We have just been introduced to using protected as well as subclasses (first system to use it) so the idea that I could still access the seat variable in floor grid went right through me. Thanks again! — DaleJV, Sep 02 '19 at 00:50

H.T. Kong · Accepted Answer · 2019-09-02T03:48:50.300

In the abstract class method(where you want to use the initialized array), you can just assume the array is already initialized. However, in the subclass, you cannot have another "Seat[][] newSeats;". So, just delete that in all sub-classes.

A quick example is as following,

//This will print 6 to the std output
public class HelloWorld{

     public static void main(String []args){
        Child test = new Child();
        System.out.println(test.getArrFirst());
     }


     public static abstract class Parent{
        int[] abc;

        public int getArrFirst(){
            return abc[1];
        }
     }

     public static class Child extends Parent{

         public Child(){
             abc = new int[10];
             abc[1] = 6;
         }
     }
}

Thank you so much for your help, answered my question very well. Just new to using subclasses as well as protected keyword so automatically thought about it as a standalone class! — DaleJV, Sep 02 '19 at 00:51

How to use a object created in a subclass of a abstract class, in the abstract class

1 Answers1