Gof design pattern

GOF
Naveen Kumar K S
Adith.Naveen@gmail.com

Introduction
¡ Design patterns represent the best practices used
by experienced object-oriented software
developers.
¡ Design patterns are solutions to general problems
that software developers faced during software
development
¡ All Design Patterns are got based on trial and
error by software engineers.

GOF?
¡ Discussed in 1994
¡ By Four people
¡ Erich Gamma
¡ Richard Helm
¡ Ralph Johnson
¡ John Vlissides
¡ To encourage people to go with reusable coding

Types of Design Patterns
¡ There are 23 design patterns which can be
classified in three categories: Creational,
Structural and Behavioral patterns.
¡ Another design pattern J2EE will be discussed in
other course

Creational Patterns
Abstract Factory Creates an instance of several families of classes
Builder Separates object construction from its representation
Factory Method Creates an instance of several derived classes
Prototype A fully initialized instance to be copied or cloned
Singleton A class of which only a single instance can exist

Structural Patterns
Adapter Match interfaces of different classes
Bridge Separates an object’s interface from its implementation
Composite A tree structure of simple and composite objects
Decorator Add responsibilities to objects dynamically
Facade A single class that represents an entire subsystem
Flyweight A fine-grained instance used for efficient sharing
Proxy An object representing another object

Behavioral Patterns
Chain of Resp. A way of passing a request between a chain of objects
Command Encapsulate a command request as an object
Interpreter A way to include language elements in a program
Iterator Sequentially access the elements of a collection
Mediator Defines simplified communication between classes
Memento Capture and restore an object's internal state
Observer A way of notifying change to a number of classes
State Alter an object's behavior when its state changes
Strategy Encapsulates an algorithm inside a class
Template Method Defer the exact steps of an algorithm to a subclass
Visitor Defines a new operation to a class without change

Singleton
¡ Singleton pattern is one of the simplest design
patterns in Java. This type of design pattern
comes under creational pattern as this pattern
provides one of the best ways to create an
object.

Factory Pattern
¡ Factory pattern is one of most used design
pattern in Java. This type of design pattern
comes under creational pattern as this pattern
provides one of the best ways to create an
object.
¡ In Factory pattern, we create object without
exposing the creation logic to the client and
refer to newly created object using a common
interface.

Abstract Factory Pattern
¡ Abstract Factory patterns work around a super-
factory which creates other factories. This factory
is also called as factory of factories. This type of
design pattern comes under creational pattern
as this pattern provides one of the best ways to
create an object.

Prototype Pattern
¡ Prototype pattern refers to creating duplicate
object while keeping performance in mind. This
type of design pattern comes under creational
pattern as this pattern provides one of the best
ways to create an object.

Bridge Pattern
¡ Bridge is used when we need to decouple an
abstraction from its implementation so that the
two can vary independently. This type of design
pattern comes under structural pattern as this
pattern decouples implementation class and
abstract class by providing a bridge structure
between them.

Filter Pattern
¡ Filter pattern or Criteria pattern is a design
pattern that enables developers to filter a set of
objects using different criteria and chaining them
in a decoupled way through logical operations.
This type of design pattern comes under
structural pattern as this pattern combines
multiple criteria to obtain single criteria.

Decorator Pattern
¡ Decorator pattern allows a user to add new
functionality to an existing object without altering
its structure. This type of design pattern comes
under structural pattern as this pattern acts as a
wrapper to existing class.

Façade Pattern
¡ Facade pattern hides the complexities of the
system and provides an interface to the client
using which the client can access the system. This
type of design pattern comes under structural
pattern as this pattern adds an interface to
existing system to hide its complexities.

Observer Pattern
¡ Observer pattern is used when there is one-to-
many relationship between objects such as if one
object is modified, its dependent objects are to
be notified automatically. Observer pattern falls
under behavioral pattern category.

Delegate Pattern
¡ Business Delegate Pattern is used to decouple
presentation tier and business tier. It is basically
use to reduce communication or remote lookup
functionality to business tier code in presentation
tier code. In business tier we have following
entities.

J2EE Patterns
¡ Presentation Tier Patterns
¡ Business Tier Patterns
¡ Integration Tier Patterns

Intercepting Filter
¡ intercepts incoming requests and outgoing
responses and applies a filter.
¡ These filters may be added and removed in a
declarative manner
¡ For an incoming request, this is often a Front
Controller

Front Controller
¡ Is a container to hold the common processing
logic that occurs within the presentation tier
¡ A controller handles requests and manages
content retrieval, security, view management,
and navigation, delegating to a Dispatcher
component to dispatch to a View.
¡ The Front Controller pattern creates central
control logic for presentation request handling.

Dispatcher View
¡ Combines a controller and dispatcher with views
and helpers to handle client requests and
prepare a dynamic presentation as the response.
¡ A dispatcher is responsible for view management
and navigation and can be encapsulated either
within a controller, a view, or a separate
component.
¡ The Dispatcher View pattern handles the request
and generates a response while managing
limited business processing.

Business Delegate
¡ Reduces coupling between remote tiers and
provides an entry point for accessing remote
services in the business tier.
¡ A Business Delegate might also cache data as
necessary to improve performance.
¡ A Business Delegate encapsulates a Session
Façade and maintains a one-to-one relationship
with that Session Façade.
¡ You want to hide clients from the complexity of
remote communication with business service
components.

Session Façade
¡ Provides coarse-grained services to the clients by
hiding the complexities of the business service
interactions.
¡ This is the same as a Façade pattern as
described in GOF Design Patterns, but just
provides an interface to a service instead of
code.

Composite Entity
¡ Implements a Business Object using local entity
beans and POJOs.
¡ When implemented with bean-managed
persistence, a Composite Entity uses Data Access
Objects to facilitate persistence.
¡ to avoid the drawbacks of remote entity beans,
such as network overhead and remote inter-
entity bean relationships.

Transfer Object
¡ You want clients to access components in other
tiers to retrieve and update data.
¡ You want to reduce remote requests across the
network.
¡ You want to avoid network performance
degradation caused by chattier applications
that have high network traffic.
¡ Reduces network traffic
¡ Simplifies remote object and remote interface

Data Access Object
¡ Enables loose coupling between the business
and resource tiers.
¡ Data Access Object encapsulates all the data
access logic to create, retrieve, delete, and
update data from a persistent store.
¡ Data Access Object uses Transfer Object to send
and receive data.

Web Service Broker
¡ Exposes and brokers one or more services in your
application to external clients as a web service
using XML and standard web protocols.
¡ A Web Service Broker can interact with
Application Service and Session Façade.
¡ A Web Service Broker uses one or more Service
Activators to perform asynchronous processing of
a request.
¡ The Web Service Broker pattern exposes and
brokers services using XML and web protocols.

Gof design pattern

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