Builder pattern

Builder PatternCopyright 2016. Jyaasa Technologies. All Right Reserved

http://jyaasa.com

Sagun ShresthaSr. Software Engineer, Jyaasa Technologies

What is Builder Pattern?

Copyright 2016. Jyaasa Technologies. All Right Reserved http://jyaasa.com

● The builder pattern is an object creation software design pattern.

● It is a pattern designed to help you configure complex objects

● It helps separate the construction of a complex object from its representation.

● So that the same construction process can create different representations.

Let’s suppose we are building a system that will support computer manufacturing business


class Computerattr_accessor :displayattr_accessor :motherboardAttr_reader :drives

def initialize(display=:crt, motherboard=Motherboard.new,drives=[ ])

@motherboard = motherboard@drives = drives@display = display

endend

class CPU# Common CPU stuff...end

class BasicCPU < CPU# Lots of not very fast CPU-related

stuff...end

class TurboCPU < CPU# Lots of very fast CPU stuff...End

# Computer’s motherboard and drive

class Motherboardattr_accessor :cpuattr_accessor :memory_size

def initialize(cpu=BasicCPU.new, memory_size=1000)@cpu = cpu@memory_size = memory_size

endend

class Driveattr_reader :type # either :hard_disk, :cd or :dvdattr_reader :size # in MBattr_reader :writable # true if this drive is writable

def initialize(type, size, writable)@type = type@size = size@writable = writable

endend

# Build a fast computer with lots of memory...

motherboard = Motherboard.new(TurboCPU.new, 4000)

# ...and a hard drive, a CD writer, and a DVD

drives = [ ]drives = << Drive.new(:hard_drive, 200000, true)drives << Drive.new(:cd, 760, true)drives << Drive.new(:dvd, 4700, false)

computer = Computer.new(:lcd, motherboard, drives)

class ComputerBuilder attr_reader :computer

def initialize @computer = Computer.new end

def turbo(has_turbo_cpu=true) @computer.motherboard.cpu = TurboCPU.new end

def display=(display) @computer.display=display end

def memory_size=(size_in_mb) @computer.motherboard.memory_size = size_in_mb end

def add_cd(writer=false) @computer.drives << Drive.new(:cd, 760, writer) end

def add_dvd(writer=false) @computer.drives << Drive.new(:dvd, 4000, writer) end

def add_hard_disk(size_in_mb) @computer.drives << Drive.new(:hard_disk, size_in_mb, true) endend

builder = ComputerBuilder.newbuilder.turbobuilder.add_cd(true)builder.add_dvdbuilder.add_hard_disk(100000)

# new computercomputer = builder.computer

class DesktopComputer < Computer # Lots of interesting desktop details omitted...End

class LaptopComputer < Computer def initialize( motherboard=Motherboard.new, drives=[] ) super(:lcd, motherboard, drives) end

# Lots of interesting laptop details omitted...end

class ComputerBuilder attr_reader :computer

def turbo(has_turbo_cpu=true) @computer.motherboard.cpu = TurboCPU.new end def memory_size=(size_in_mb) @computer.motherboard.memory_size = size_in_mb endend

class DesktopBuilder < ComputerBuilder

def initialize @computer = DesktopComputer.new end

def display=(display) @display = display end

def add_cd(writer=false) @computer.drives << Drive.new(:cd, 760, writer) end

def add_dvd(writer=false) @computer.drives << Drive.new(:dvd, 4000, writer) end

def add_hard_disk(size_in_mb) @computer.drives << Drive.new(:hard_disk, size_in_mb, true) endend

class LaptopBuilder < ComputerBuilder

def initialize @computer = LaptopComputer.new end

def display=(display) raise "Laptop display must be lcd" unless display == :lcd end

def add_cd(writer=false) @computer.drives << LaptopDrive.new(:cd, 760, writer) end

def add_dvd(writer=false) @computer.drives << LaptopDrive.new(:dvd, 4000, writer) end

def add_hard_disk(size_in_mb) @computer.drives << LaptopDrive.new(:hard_disk, size_in_mb, true) endend

Structure

Participants● Builder

○ Specifies an abstract interface for creating parts of a Product object.

● ConcreteBuilder○ Constructs and assembles parts of the product by

implementing the Builder interface.○ Defines and keeps track of the representation it creates.○ Provides an interface for retrieving the product

● Director○ Constructs an object using the Builder interface.

● Product○ Represents the complex object under construction.

ConcreteBuilder builds the product's internal representation and defines the process by which it's assembled.

○ Includes classes that define the constituent parts, including interfaces for assembling the parts into the final result.

Collaboration

● The client creates the Director object and configures it with the desired Builder object.

● Director notifies the builder whenever a part of the product should be built.

● Builder handles requests from the director and adds parts to the product.

● The client retrieves the product from the builder.

def computer raise "Not enough memory" if @computer.motherboard.memory_size < 250 raise "Too many drives" if @computer.drives.size > 4 hard_disk = @computer.drives.find {|drive| drive.type == :hard_disk} raise "No hard disk." unless hard_disk @computerend

Building Sane Object

Thank you


Builder pattern

Software

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