SE450: Review: Pattern Summary: Collections [24/25]

Null Object: Replace null reference with an object with trivial behavior.

Composite: Make collections of objects have the same interface as single objects.

Internal Iterator: Pass a function into a collection. The collection runs the function on each element. Not on final exam.

External Iterator: Recieve an object from a collection; use the object to access the elements in the collection. Not on final exam.

Visitor: double dispatch an iterator, typically an internal iterator over a composite.