The Command pattern

At this point, Phoebe has designed two different models of the robotic arm. One set of arms was large and bolted to the floor. These arms were stationary. The second set of arms was mounted on tracks and could move. These were mainly used for moving the parts, materials, and partially finished bicycles around to different stations. Once at a station, the larger arms would do most of the real work.

The larger arms that were bolted to the floor had interchangeable attachments that allowed them to perform different tasks. Phoebe designed this behavior based on the Decorator pattern. Remember, a decorator allows you to add new behavior to an existing class without you having to modify it directly. This is done by creating a new class that wraps around the structure of the original class, then adds the additional behavior. In this case, the decorators are physical hardware. Phoebe marveled at the patterns. She understood how working with the patterns might be considered...