Creating an array of subclasses of a class

Question

I'm trying to store all subclasses of A which are constructed by super() in the array child (in this case B). All the children are in the same package. This is my approach but I don't know how the class could store itself inside an array or pass itself as argument to super().

class A {
  static int i = 0;
  A[] child = new A[10]
  int someval;
  A(int val){
    someval = val;
    child[i] = ???;
    i++;
  }
}
class B extends A{
   B(){
     super(val);
   }
}

Is this even Possible? With my approach B will only be added when a new B() is created? Is it possible to get a complete array without creating a new object?

this refers to the current instance.

Dave Newton
– Dave Newton

2018-01-12 16:40:50 +00:00
Commented Jan 12, 2018 at 16:40 — Dave Newton
– Dave Newton, Commented Jan 12, 2018 at 16:40
also, make the "child" array static

Sean F
– Sean F

2018-01-12 16:41:51 +00:00
Commented Jan 12, 2018 at 16:41 — Sean F
– Sean F, Commented Jan 12, 2018 at 16:41

David Lavender · Accepted Answer · 2018-01-12 16:43:05Z

3

public class A {
    private static final List<A> instances = new ArrayList<>();

    public A() {
        instances.add(this);
    }

    public static List<A> getInstances() {
        return instances;
    }
}

Now A.getInstances() can be called whenever you like, and will contain instances of anything that extends A.

answered Jan 12, 2018 at 16:43

David Lavender

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2 Comments

derry Over a year ago

Do I have to use a list? I rather do it with an array as i did not read about lists yet.

user6073886 Over a year ago

@derry Lists automatically grow, arrays are fixed size. So unless you want to implement logic to constantly create new arrays when the number of instances gets to big for your array you should go with a List. (As an ArrayList already has that work done for you)

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