desing pattern prototype-factory method, prototype and builder

Design Pattern

Introduction Factory Method, Prototype & Builder Design

Pattern

-ParamiSoft Systems Pvt. Ltd.

Agenda• Factory Method Pattern

o Introductiono When to consider?o Example o Limitations

Prototype Patterno Introductiono Applicability o Consequences o Example

Prototype Patterno Introductiono Example o Discussion


The Gang of Four: Pattern CatalogCreational

Abstract FactoryBuilderFactory MethodPrototypeSingleton

StructuralAdapterBridgeCompositeDecoratorFaçadeFlyweightProxy

BehavioralChain of ResponsibilityCommandInterpreterIteratorMediatorMementoObserverStateStrategyTemplate MethodVisitor

Patterns in red we will discuss in this presentation


Factory Method



• Name: Factory Method• Intent: Define an interface for creating an object,

but let subclasses decide which class to instantiate. Defer instantiation to subclasses.

• Problem: A class needs to instantiate a derivation of another class, but doesn't know which one. Factory Method allows a derived class to make this decision.

• Solution: Provides an abstraction or an interface and lets subclass or implementing classes decide which class or method should be instantiated or called, based on the conditions or parameters given.

Factory Method


When to consider?• When we have a class that implements an

interface but not sure which object, which concrete instantiation / implementation need to return.

• When we need to separate instantiation from the representation.

• When we have lots of select and switch statements for deciding which concrete class to create and return.


Factory Says

Define an interface for creating an object, but let subclasses decide which class to instantiate


public interface ConnectionFactory{public Connection createConnection();

}class MyConnectionFactory implements ConnectionFactory{

public String type;public MyConnectionFactory(String t){

type = t; }

public Connection createConnection(){if(type.equals("Oracle")){

return new OracleConnection(); }else if(type.equals("SQL")){

return new SQLConnection(); }else{ return new MySQLConnection(); }

}}

Implementation: ConnectionFactory


public interface Connection{public String description();public void open();public void close();

}class SQLConnection implements Connection{

public String description(){ return "SQL";} }class MySQLConnection implements Connection{

public String description(){ return "MySQL” ;} }class OracleConnection implements Connection{

public String description(){ return "Oracle"; } }



class TestConnectionFactory{public static void main(String[]args){

MyConnectionFactory con = new MyConnectionFactory("My SQL");

Connection con2 = con.createConnection();System.out.println("Connection Created: ");System.out.println(con2.description());

}}



• Refactoring an existing class to use factories breaks existing clients.

• Since the pattern relies on using a private constructor, the class cannot be extended

• if the class were to be extended (e.g., by making the constructor protected—this is risky but feasible), the subclass must provide its own re-implementation of all factory methods with exactly the same signatures.

Limitations

Prototype Design Pattern


Prototype Design Pattern

Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype


Structure


Applicability


• Avoid subclasses of an object creator in the client application

• Avoid the inherent cost of creating new object in the standard way eg. Using new keyword

• Alternative to Factory Method and Abstract Factory.

• Can be used to implement Abstract Factory.• To avoid building a class hierarchy of factories.• Can be used when loading classes dynamically• Often can use class objects instead.

Consequences


• Add/Remove prototypes at runtime.• Specify new prototypes by varying data.• Specify new prototypes by varying

structure.• Less classes (less sub-classing!)• Dynamic class loading.

Psudocode


class WordOccurrences is field occurrences is The list of the index of each occurrence of the word in the text.

constructor WordOccurrences(text, word) is input: the text in which the occurrences have to be found input: the word that should appear in the text Empty the occurrences list for each textIndex in text isMatching := true for each wordIndex in word if the current word character does not match the current text character then isMatching := false if isMatching is true then Add the current textIndex into the occurrences list

Psudocode


method getOneOccurrenceIndex(n) is input: a number to point on the nth occurrence. output: the index of the nth occurrence. Return the nth item of the occurrences field if any.

method clone() is output: a WordOccurrences object containing the same data. Call clone() on the super class. On the returned object, set the occurrences field with the value of the local occurrences field. Return the cloned object.

text := "The prototype pattern is a creational design pattern in software development first described in design patterns, the book."word := "pattern"searchEngine := new WordOccurrences(text, word)anotherSearchEngine := searchEngine.clone()

Builder Design Pattern



• Name: Builder • Intent: The intent of the Builder design pattern is

to separate the construction of a complex object from its representation. By doing so, the same construction process can create different representations

Builder


The builder pattern is an object creation design pattern. Unlike the abstract factory and factory method pattern whose intention is to enable polymorphism, the intention of the builder pattern is to find a solution to the telescoping constructor anti-pattern. The telescoping constructor anti-pattern occurs when the increase of object constructor parameter combinations leads to an exponential list of constructors. Instead of using numerous constructors, the builder pattern user another object. A builder that receives each initialization parameter step by step and then returns the resulting constructed object at once

Description

Psudocode


class Car is Can have GPS, trip computer and various numbers of seats. Can be a city car, a sports car, or a cabriolet.

class CarBuilder is method getResult() is output: a Car with the right options Construct and return the car.

method setSeats(number) is input: the number of seats the car may have. Tell the builder the number of seats.

method setCityCar() is Make the builder remember that the car is a city car.

method setCabriolet() is Make the builder remember that the car is a cabriolet.

method setSportsCar() is Make the builder remember that the car is a sports car.

Psudocode


method setTripComputer() is Make the builder remember that the car has a trip computer.

method unsetTripComputer() is Make the builder remember that the car does not have a trip computer.

method setGPS() is Make the builder remember that the car has a global positioning system.

method unsetGPS() is Make the builder remember that the car does not have a global positioning system.

Construct a CarBuilder called carBuildercarBuilder.setSeats(2)carBuilder.setSportsCar()carBuilder.setTripComputer()carBuilder.unsetGPS()car := carBuilder.getResult()

Discussion


• Factory Method: delegate to subclasses.• AbstractFactory, Builder, and Prototype:

delegate to another class.• Prototype: reduces the total number of

classes.• Builder: Good when construction logic is

complex.

References

Linkso http://en.wikipedia.org/wiki/Factory_method_patterno http://en.wikipedia.org/wiki/Prototype_patterno http://en.wikipedia.org/wiki/Builder_patterno http://sourcemaking.com/design_patterns

Linkso Design Patterns in Ruby – Russ Olseno Head First Design Patterns – Elisabeth Freeman, Eric Freeman, Bert Bates and Kathy

Sierra


http://en.wikipedia.org/wiki/Factory_method_pattern

http://en.wikipedia.org/wiki/Factory_method_pattern

http://sourcemaking.com/design_patterns

If(Questions){

Ask; }else {

Thank you; }


desing pattern prototype-factory method, prototype and builder

Technology

prototype paramisoft

psudocode paramisoft

structure paramisoft

class objects

class myconnectionfactory

class sqlconnection

class oracleconnection

class mysqlconnection