Make a class use another class?

[GoToLoop]

I’ve got this example of a class named ArrayQueue which is implemented using :
public class ArrayQueue<E> implements Queue<E>, Cloneable, Serializable {

LinkedList vs ArrayList

It works for me for some reason. In order to test ArrayQueue, I’ve picked 2 old sketches using container ArrayDeque as a Queue: Docs.Oracle.com/en/java/javase/11/docs/api/java.base/java/util/ArrayDeque.html And then replaced that w/ my own ArrayQueue, and both sketches were still perfectly OK:

https://gist.github.com/GoToLoop/145418d1dfb062c7c41a630bce5b8374