GoF Design Patterns Summary

GoF Design Patterns Summary

Design Pattern, is a general reusable solution to a commonly occurring problem within a given context in software design. Design patterns help you show the path how the similar problem was solved. Each Design Pattern should have a correct NAME, INTENT and MOTIVATION. Name of the Pattern help you understand what problem it is trying to address, Intent will help you dig deeper into it. Motivation of this pattern might help you understand the scenario / context when you can apply this pattern. There are too many patterns available in the industry they are broadly divided into these categories.

These are the categories of GoF Patterns( Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides). The best book to read about these Design Patterns is – Design Patterns: Elements of Reusable Object-Oriented Software written by GoF (Gang of Four).

Apart from these categories, we have different categories like Architectural patterns, concurrency patterns, Integration Patterns, J2EE Patterns etc.

Below is the quick reference of Design Pattern and It’s example and the keywords you should be able to remember to figure out the pattern. This list helps you easily figure out the pattern which you can apply in the scenario you are looking for.

Note: This notes is not for a person who doesn’t know Design patterns. This is more like a quick reference guide to refresh your Design patterns. I hope my notes would help you all.

Pattern Name Example Keywords to Remember
Creation Patterns
Family of Factories Different sub types
     – Factory Method  XML reader create No Dependencies in creation
     – Factory JDBC driver initialization Common Dependencies in creation
     – Abstract Factory ADO .net provider factory Sub type specific dependencies to create
Builder String and String buffer Different ways to create same object
Prototype Clonable Impl of java Clone / re use construction logic
Singleton Configuration Manager / Cache Manager Only one instance
Multiton HTTP Session Context specific singleton
Structural Patterns 
Adapter Java connector Architecture, Power Adapter, Display Adapter
SQL Data adapter in DB
Not compatible, Integration, External, conversion, 3rd party
Bridge DB Manager class using IDB connection instead of SQL Connection,
USB 2.0 specification, Mobile SIM interface
HTTP 1.1 specification (Browser /Web Server)
Permutations n combinations, specificatons
Composite XML tree Tree, Hierarchy
Decorator IO Streams, CSS styling Add more to Objects
Facade Controller in MVC, System/ Car startup, coffee vending machine, money transfer btw accounts, Orchestrator Co-ordination, Hide the complexity
Fly Weight Pool (Connection pool, thread pool etc) Re use fine grained Obj, pooling
Proxy Internet proxy server, Download Accelerator, web Service Proxy Add more to types, wrapper without breaking compatibility
Behavioral Patterns
Chain of Responsibility AC filters, Exception handling, supply chain management, event bubling, servlet filters, server.transfer in jsp pipe lined work, Hierarchical execution, do and delegate/fwd
Command  JDBC statement. execute(DML, DDL, DCL), struts actions in controllers  set of actions to be executed
Iterator For Each loop, Iterator interface impl, JDBC result set, Video Streaming, Agile development, paginated results Step by Step or phase by Phase
Interpreter Expression evaluation, Rule validation  lexical analysis ,Rule Engines
DB transactions, windows hibernate, restore points, backup and restore DB,
versioning systems, undo/ redo in word, back n fwd in browser
Maintaining State, Restore,
Distributed transaction coordinator, JTA/ JTS (java transaction) Real estate/ Stock brokers, controls communication between windows apps, bit torrents, chat clients/servers, iCloud to sync the data, mobile service providers
 Data Exchange with different formats
Observer DB triggers, fire alarms, mouse and keyboard Events, Eventing, notification
Strategy Collection uses comparable interface to compare different types of sorting, different types of credit card validation algorithms, different compression algos, Defining interfaces, stopping “what if” analysis
State Water object behaves differently in solid and liquid states, actors and roles, DB and TCP connections states, Bank A/c or Membership card state(gold,silver etc)
Changing behavior of an Object
          Avoiding if condition based logic
Template method Servlet life cycle Life cycle
Visitor GC of JVM  Repeated jobs with involvement of external components.


All your feedback is welcome.

Happy Reading 🙂



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