Object-oriented – Multiple instance of the same class

I don't know why you need to keep a list of all instances of a class.

That would cause memory leakage since those objects will never be disposed of, since the list will still be referencing them after no other class does.

But if you really want to follow that route:

1. Use the Factory pattern. A factory class with methods that instanciate the class and return the objects. That way you have a centralize point to control the instantiations.
2. Use the Singleton pattern to hold a list or lists that hold the instances.
3. Make the factory put each object of a certain type in a list after creating them.

By the way: constructors are inherited.

The principle reasons for not following the ItemContainer->getItems() approach and returning an array are:

1. The initial implementation is likely to just return a reference to the original array, which would then allow the caller to modify the underlying collection. This is considered bad practice.
2. The next work around is then to make a copy of the array and return that instead. This is bad because a caller may think they are still modifying the underlying collection, and it is also expensive for large collections.

If the caller really wants to have a copy of the array, then itemContainer->cloneItems() is much clearer, and less likely to be used inappropriately.

If the caller is just wanting to have a single item, then providing a

itemContainer->getItem(index && key)

is clear and efficient

If the caller is wanting to iterate over the items, then providing a

itemContainer->getItemIterator()

is clearer. Depending on the language you may implement

itemContainer->VisitItems(visitor)

where visitor is a visitor class, delegate or function pointer.

Hopefully, I've given you some ideas on how this can be approached differently