How to Design the Following Data Structure in Java

Question

I have a list, L1<A> , of about 60 to 120 objects, A , that themselves contain a list L2<D> of objects, D .

The L2<D> s are identical for all A .

The user can upload new D s, and every time the program has to go through all of L1 and add add the new D to each L2 . Obviously, I would rather have a master L2 that can just be updated once and have every A refer to that list, but I don't want to make some kind of global variable L2 .

If I make a single instance of L2 , do I just have to pass L2 to every A in L1 , or can I get each A to refer to the single L2 without using a global variable?

Answer 1

static variable is what you are looking for.

public class A {
    private static final List<D> l2 = new ArrayList<>();

    public void addD(D d) {
        l2.add(d);
    }
}