Class Diagram Example: GoF Design Patterns - Decorator


Decorator design pattern is one of the Gang of Four (GOF) design patterns. Decorator design pattern allows for the dynamic wrapping of objects in order to modify their existing responsibilities and behaviors.

You can create your own class model by editing this Decorator design pattern template. Click Use this Template to start, or click Create Blank to create a new class diagram.

What is Class Diagram?

A class diagram is primarily designed for developers to provide the conceptual model and architecture of the system being developed. A class diagram provides the overview and structure of a system in terms of classes, attributes and methods, and the relationships between different classes.

Class diagrams are at the heart of UML. A class diagram carries different information depending on the phase of the development process and the level of detail being considered. As development progresses, a class diagram moves towards the implementation domain, which is familiar to software developers. Class diagrams are a vital part of any software development project and they form the foundation of all software products.

Guidelines for creating Class Diagram?

  1. Identify classes
    • a. From domain analysis such as textual analysis
    • b. From CRC cards
    • c. From use case description
    • d. From sequence diagram or use case scenarios
  2. Give analysis a name and a brief description which could be done through terms and glossary
  3. Structure classes in the right places of the diagram and related them with simple relationships
  4. As the development move forward, detail the class with attributes and operations, this often done in conjunction with use case and sequence diagrams
  5. Refine the class diagram with inheritance for future reuse
  6. Elaborate the details which is helpful for implementation such as accessibility, rules, constraints and etc.
  7. Put related classes into packages to form your software architecture

Why do we need Class Diagram?

Class diagrams are useful in many stages of system design:

  1. Analysis stage - a class diagram can help you to understand the requirements of your problem domain and to identify its components.
  2. Design stage - you can refine your earlier analysis and conceptual models into class diagrams that show the specific parts of your system, user interfaces, logical implementations, and so on.v
  3. Detailed design stage - the class diagrams that you create during the early stages of the project contain classes that often translate into actual software classes and objects when you write code.v
  4. Implementation stage - you can use class diagrams to convert your models into code and to convert your code into models.

Your class diagrams then become a snapshot that describes exactly how your system works, the relationships between system components at many levels, and how you plan to implement those components.

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