Lecture 6A

Presentation Topic

• Introduces the concept of Design Patterns (DP).
• Covers a practical scenario.
• Focuses on implementing DP in Java.
• Outlines the next steps and conclusion.
• Involves collaborative coding using DP in Java via VS (Visual Studio) Code Live Share.

From Programming to Coding

• Programming involves logic, applied math, and abstraction.
• Coding is about technical details, including syntax and patterns.

Pattern Identification

• Patterns involve solving problems.
• If a problem is unprecedented, it is a chance to be a pioneer.
• If not, there are two options: be innovative or review and reuse solutions.

Design Patterns (DP) – The Idea

• If someone were an architect, what would the idea be for projecting new spaces?
• Christopher Alexander is related design patterns
• Recurring problems have already good solutions, which can be found in catalogs.

Design Patterns (DP) – The Beauty

• There is beauty in patterns; even simple patterns can be combined to create beautiful things.
• Reuse is key, but the way these patterns are used is essential to create the expected results.

Design Patterns in Computing

• Developers should use Design Patterns (DP).
• Programs are based on abstractions used to solve problems.
• Modern programming languages like C++, C#, PHP, Python, and Java all use DP.
• They are based in modularization and reuse.
• They can work with the OO (Object Oriented) paradigm, creating classes and objects.
• Patterns identify and specify abstractions above single classes, instances, or components.
• Design patterns are not based on the "copy and paste" culture, but in a strategic approach to problem-solving.

Why should use DP?

• DP provide definitions to help define better solutions with easy maintenance.
• They capture software engineering experiences.
• DP provide transparency to the design of an application.
• Design patterns do not guarantee an absolute solution but clarify system architecture, enabling better system building.

How to Use DP

• Main strategy involves understanding the problem, imagining the solution, identifying the best practice, and applying the right pattern.
• A design pattern is a documented best practice, or core of a solution, applied successfully in different environments to solve recurring problems.
• UML (Unified Modeling Language) is useful for initial analysis before coding.
  • Needs should initially be identified from the user's perspective with a Use-Case Diagram.
  • The next step is entities – static modeling via Class Diagram.
  • Should continue with behavior through dynamic modeling (Sequence or Collaboration diagrams).

Defining a DP

• A template is used.
• Template Attributes:
  • Name – How identified
  • Purpose – What does it perform
  • Context – Where applied
  • Known uses – Examples how to use
  • Implementation – Rules/Tech
  • Consequences – Results expected.

Initial Problem - Mini-shop

• This is a practical scenario.
• An online shop requires a system supporting different customers and including products in a cart.
• Each customer has only one cart.
• At the end, each customer must finish the shop and do the payment according to customer credit.

Why is a pattern needed?

• It is needed to connect different entities using a better strategy.
• When needing an interface, is about a "middleware" layer between internal/external entities.
• Relates to architectural vision, not just a programming concept.

Using Patterns Here - Mini-shop

• Think of using a pattern.
• Entities like customers, products, and carts must connect and be managed by someone.
• Goal is to the pattern's only point to encapsulate complexity.
• Design patterns are proposed by professional developers.

Knowing the first Pattern: Facade

• One of the 23 classical patterns created by the "Gang of Four."
• Gamma, Helm, Johnson, and Vlissides, created it in 1993.
• Involves classes invoking a controller/facade, which manages the entire process.

Thinking the Model

• Think of the models
  • Customer with a String name and float credit.
  • Products with a String name and float unitPrice.
  • Cart of Customer owner, List of products, and float totalPrice.

Thinking the Pattern (Façade)

• The purpose is to call entities and create a "sequence" of methods for all activities.
• There is a need that is available for any client to create new shop online.

Domain Classes

• Shows code examples for creating domain classes in Java.
• Code snippets provided for classes, Customer, Product and OrderFacade.

What is a Facade Class?

• Shows Java code for setting up the Facade class.

Client (main) Class

• Java lines of code.
• Shows a customer with customer credit, gift card and cart totals.

Conclusion World of Patterns

• Patterns are used everywhere.
• Do know that even minimal code uses patterns.
• Define components (classes), behaviors (methods) and relations (inheritance).

GRASP (General Responsibility Assignment Software Patterns Design)

• Helpful to continue progress. Examples of principles includes such as, "information expert, low coupling" + High cohesion and Polymorphism - All are key to progressing in this career.
• Patterns and practices are developed by writing the code in a way that's correct.

World of Patterns (2) Language Patterns

• Several programming languages like Java incorporate the patterns internally.
• Where: - Java.util (used in Collections). -Java.util (used in listeners). - Java.lang (see StringBuilder). - Java.util(see Collections). - .Javax.faces (used in JSF).
• Important note that learning these languages, not only need to learn syntax, but contact alternatives using patterns.

World of Patterns (3)

• Enterprise Patterns is also used for defining architectures.
• MVC (Model View Controller) is an example of enterprise patterns

Being a Good Professional...

• DP are like swiss pocketknife: formidable and know use.
• Summary: DP are best practices help challenge
• Use programming guide to languages and architecture to do DP.