What is a Design Pattern
"Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice"
- Cristopher Alexander -
"Is a general resuable solution to common ocurring problems. It is a description of template for how to solve a problem in different situations"
- Wikipedia -
Prerequisites & Basic Principles
These are the basic principles one should be concerned before applying patterns.
- Use Object Oriented language
- Use of Abstraction
- Use of Encapsulation
- Use High Cohesion
- Use Loose Coupling
- Use Open - Closed priniple
- Use Separation Of Concerns
- Use Dependency Inversion
- Separate volatile from Stable components
- Use Interfaces simple, clear and course grained
- Use Composite reuse instead of inheritance
Most Famous Patterns
- Layers Pattern
- Tiers Pattern
- Model-View-Controller Pattern
- P.A.C. Architectural Pattern
The Layers Pattern
The Layers pattern structures applications so they can be decomposed into groups of subtasks, each group represents a particular level of abstraction.
The Tiers Pattern
Tiers describe how a distribute application is decomposed into modules to reduce the coupling and imprive the system flexibility. This permits each tier to be modified or enhanced without affecting other tiers. Example for the JAVA world.
The MVC Pattern
The MVC Pattern separates concerns in data presentation, processing and storage. This pattern is useful for emphasizing separation of concerns.
The PAC pattern is a further refinement of the Model View Controller pattern. For complex UIs, it creates a hierarchy of interacting, cooperating agents. Each agen is its own "mini" MVC component. It differs from MVC in that within each agent, the presentation and abstraction are completely separated. This pattern enforces decoupling and separation of concerns.
Here is a list where you can find more design patterns.
- Hardware Configuration Patterns
- Software Design Patterns
- GOF Patterns (Gang Of Four Patterns)
- Java EE Patterns
- Architecture Patterns
- Buschmann, et al. Patterns
- Enterprise Architecture Integration Patterns
- Enterprise Application Architecture Patterns
- Antipatterns: to avoid common design traps
- Analysis Paralysis
- Cash Cow
- God Object
GOF Catalog Of Design Patterns
24 Design Patterns that will help you solve the majority of your problems.
- Abstract Factory
- Chain Of Responsability
- Factory Method
The JAVA language defines another set of design patterns.
- DAO (Data Access Object)
- Service Locator
- Transfer Object
- Application Service
- Business Delegate
- Value List Handler
- Front Controller
- Application Controller
- Context Object
- View Helper
Using Patterns Across a Network
When working in a network, the Command Pattern is an example of design pattern to send messages from the client to the server.
Several patterns can be combined to architect your solution as show in the picture.
- Oracle JEE Student Guide for JEE Architects
- Design Patterns: Elements Of Reusable Object-Oriented Software
- Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides