implementing the singleton design pattern

8/3/2019 Implementing the Singleton Design Pattern

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Singleton Design Pattern

There Can Be Only One!


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OverviewObjective

Learn how to use the singleton design pattern.

Requirements Basics of PHP

Basics of ProdigyView

Estimated Time

7 minutes

www.prodigyview.com
http://www.prodigyview.com/http://www.prodigyview.com/


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Follow Along With Code Example1. Download a copy of the example code at

www.prodigyview.com/source.

2.Install the system in an environment you feelcomfortable testing in.

3.Proceed to examples/data/Singleton.php
http://www.prodigyview.com/sourcehttp://www.prodigyview.com/source


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What is a Singleton DesignPattern?

The singleton design pattern may be one of the mostcommon design patterns in PHP. The pattern can bedescribed as restricting the instances of an object.

In other words, the keyword new may only be used onceon this object.

There may come situations when developing that you willonly want one instance of an object to be used and only

use the same instance at various points in your code. Thiswill be accomplished using the singleton design pattern.


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Singleton Visual

SingleInstance

NewInstance

NewInstance

NewInstance

NewInstance

All new instances call a single instance


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Protect The ConstructorTo force a class to be used as a singleton, we cannot allow theclass to be instantiated with the key word new. To prevent thatmake the__constructor protected. Also extend PVObject orPVPatterns to the class.

DO NOT MAKE THE CONSTRUCTOR PRIVATE OR THISWILL NOT WORK.

Extend PVObject

ProtectedConstructor


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Object::getInstance()In our previous slide we extended PVObject class. UsingPVObject or PVPatterns class, they both have a methodcalled getInstance().

This method will create a single instance of the object andstore it. Anytime that getInstance() is called, it willretrieve the same instance of the object.

The getInstance() is a replacement for the new

operator, meaning new Object will never be used.


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The RidesSo we have our ticket class. Now lets make some classesthat act as the rides. These classes get the instance of the

ticket class with the getInstance() method.

Get the objects instance



Call the objects method




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Using our Tickets Ticket Class that has tickets check

Rides that use the ticket class check

Instance of the ticket class check

We are ready to start taking the tickets and enjoying theride.


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ResultsYour results may look something similar to this:


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An ExplanationHere is what happened to make the result. When the instanceof the class was created, all the variables in that classbecomes usable.

Because only one instance is made, the variables inside theobject are always in the same state. Even though the instancewas being used inside different classes, it was still the sameinstance and therefore the same variables being used.

In our example tickets, we are always subtracting from thesame ticket variable inside of the Tickets object because weare only using one instance of ticket.


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API ReferenceFor a better understanding of the Collections and the

Iterator, check out the api at the two links below.

PVStaticPatterns

PVPatterns

www.prodigyview.com

More Tutorials

For more tutorials, please visit:

http://www.prodigyview.com/tutorials
http://api.prodigyview.com/api/package/prodigyviewdata-package/pvstaticpatterns-classhttp://api.prodigyview.com/api/package/prodigyviewdata-package/pvpatterns-classhttp://www.prodigyview.com/http://www.prodigyview.com/tutorialshttp://www.prodigyview.com/tutorialshttp://www.prodigyview.com/tutorialshttp://www.prodigyview.com/tutorialshttp://www.prodigyview.com/http://api.prodigyview.com/api/package/prodigyviewdata-package/pvpatterns-classhttp://api.prodigyview.com/api/package/prodigyviewdata-package/pvstaticpatterns-class

implementing the singleton design pattern

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