Designing with Patterns - Essay Example

This paper illustrates that the Composite design pattern perfectly suites the requirements of the Solent Cinemas booking system as well as the initial design given in the case study. Let us take a closer look at the classes represented in the class diagram. The ones below (directly taken from the design in the case study class diagram) are of particular interest with respect to the composite pattern: The class: Solent Cinemas holds a list of holds a list of all the cinemas in the chain and undertakes to the schedule of new films into the cinemas.

The class: Cinema holds a list of all its Screens. This shows a clear parent-child relationship existing between the two classes which are the essence of the composite design pattern. The diagram below of the two classes depicts the composition relation existing between the two classes i.e., the class Solent Cinemas is composed of objects of the class Cinemas. This is an interesting one and needs more elaboration. It looks as if the two classes are redundant, yet the class diagram shows a composition connection between the two.

By definition from the case study, the film class does the work of scheduling a show. The Show class essentially consists of the Film object but it also works in close association with the Ticket class, the Reservation class and the Screen class via the Show Schedule class. A good encapsulation rule is followed here to separate the Film and Show classes so the Film class’ responsibilities are maintained privately and the Show being compositely linked to the Film class takes the necessary details so that, for instance, the reservation class associated with the Show class gets on display only the necessary information, with the rest hidden in the Film class.

 The observer is a Behavioral Design Pattern and focuses on the communication patterns between objects. The Observer pattern assumes that the object containing the data is separate from the objects that display the data and that these display objects observe changes in that data.  When we implement the Observer pattern, we usually refer to the data as the Subject and each of the displays as Observers. Each of these observers registers its interest in the data by calling a public method on the Subject.

Then, each observer has a known interface that the subject calls when the data change.