Composite Pattern
-The pattern consists of three classes: the Composite (the node that can have children), the Leaf (no children), and the Component, which is a superclass extended by both the Composite and Leaf.
-The Composite has a collection of Components, so that the Composite class can loop through those Components without keeping track of whether the Component is actually a Composite or a Leaf.
-The Composite also has an addComponent method so that Components can be added to its contents.