What is the difference between public private and protected

Question

When and why should I use public  private  and protected functions and variables inside a class  What is the difference between them   Examples      Public public  variable  public function doSomething                    Private private  variable  private function doSomething                    Protected protected  variable  protected function doSomething

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Visibility Scopes with Abstract Examples    Makes easy Understanding  This visibility of a property or method is defined by pre-fixing declaration of one of three keyword  Public  protected and private   Public   If a property or method is defined as public  it means it can be both access and manipulated by anything that can refer to object    Abstract eg  Think public visibility scope as  public picnic  that anybody can come to    Protected   when a property or method visibility is set to protected members can only be access within the class itself and by inherited  amp  inheriting classes   Inherited - a class can have all the properties and methods of another class     Think as a protected visibility scope as  Company picnic  where company members and their family members are allowed not the public  It s the most common scope restriction    Private   When a property or method visibility is set to private  only the class that has the private members can access those methods and properties Internally within the class   despite of whatever class relation there maybe    with picnic analogy think as a  company picnic where only the company members are allowed  in the picnic  not family neither general public are allowed

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You use   public scope to make that property method available from anywhere  other classes and instances of the object   private scope when you want your property method to be visible in its own class only   protected scope when you want to make your property method visible in all classes that extend current class including the parent class    If you don t use any visibility modifier  the property   method will be public  More   For comprehensive information   PHP Manual - Visibility

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Public   When you declare a method  function  or a property  variable  as public  those methods and properties can be accessed by    The same class that declared it  The classes that inherit the above declared class  Any foreign elements outside this class can also access those things    Example    lt  php  class GrandPa       public  name  Mark Henry       A public variable    class Daddy extends GrandPa    Inherited class       function displayGrandPaName                 return  this- gt name     The public variable will be available to the inherited class              Inherited class Daddy wants to know Grandpas Name  daddy   new Daddy  echo  daddy- gt displayGrandPaName       Prints  Mark Henry      Public variables can also be accessed outside of the class   outsiderWantstoKnowGrandpasName   new GrandPa  echo  outsiderWantstoKnowGrandpasName- gt name     Prints  Mark Henry      Protected   When you declare a method  function  or a property  variable  as protected  those methods and properties can be accessed by   The same class that declared it  The classes that inherit the above declared class    Outsider members cannot access those variables   Outsiders  in the sense that they are not object instances of the declared class itself   Example    lt  php  class GrandPa       protected  name    Mark Henry      class Daddy extends GrandPa       function displayGrandPaName                 return  this- gt name             daddy   new Daddy  echo  daddy- gt displayGrandPaName       Prints  Mark Henry    outsiderWantstoKnowGrandpasName   new GrandPa  echo  outsiderWantstoKnowGrandpasName- gt name     Results in a Fatal Error   The exact error will be this      PHP Fatal error   Cannot access protected property GrandPa   name     Private   When you declare a method  function  or a property  variable  as private  those methods and properties can be accessed by    The same class that declared it    Outsider members cannot access those variables  Outsiders in the sense that they are not object instances of the declared class itself and even the classes that inherit the declared class   Example    lt  php  class GrandPa       private  name    Mark Henry      class Daddy extends GrandPa       function displayGrandPaName                 return  this- gt name             daddy   new Daddy  echo  daddy- gt displayGrandPaName       Results in a Notice    outsiderWantstoKnowGrandpasName   new GrandPa  echo  outsiderWantstoKnowGrandpasName- gt name     Results in a Fatal Error   The exact error messages will be      Notice  Undefined property  Daddy   name   Fatal error  Cannot access private property GrandPa   name     Dissecting the Grandpa Class using Reflection  This subject is not really out of scope  and I m adding it here just to prove that reflection is really powerful  As I had stated in the above three examples  protected and private members  properties and methods  cannot be accessed outside of the class    However  with reflection you can do the extra-ordinary by even accessing protected and private members outside of the class   Well  what is reflection      Reflection adds the ability to reverse-engineer classes  interfaces    functions  methods and extensions  Additionally  they offers ways to   retrieve doc comments for functions  classes and methods    Preamble  We have a class named Grandpas and say we have three properties  For easy understanding  consider there are three grandpas with names    Mark Henry John Clash Will Jones   Let us make them  assign modifiers  public  protected and private respectively  You know very well that protected and private members cannot be accessed outside the class  Now let s contradict the statement using reflection   The code   lt  php  class GrandPas      The Grandfather s class       public      name1    Mark Henry       This grandpa is mapped to a public modifier     protected   name2    John Clash       This grandpa is mapped to a protected  modifier     private     name3    Will Jones       This grandpa is mapped to a private modifier       Scenario 1  without reflection  granpaWithoutReflection   new GrandPas     Normal looping to print all the members of this class echo   Scenario 1  Without reflection lt br gt    echo  Printing members the usual way    without reflection  lt br gt    foreach  granpaWithoutReflection as  k  gt  v        echo  The name of grandpa is  v and he resides in the variable  k lt br gt       echo   lt br gt      Scenario 2  Using reflection   granpa   new ReflectionClass  GrandPas       Pass the Grandpas class as the input for the Reflection class  granpaNames  granpa- gt getDefaultProperties       Gets all the properties of the Grandpas class  Even though it is a protected or private    echo   Scenario 2  With reflection lt br gt    echo  Printing members the  reflect  way   lt br gt     foreach  granpaNames as  k  gt  v        echo  The name of grandpa is  v and he resides in the variable  k lt br gt        Output    Scenario 1  Without reflection Printing members the usual way    Without reflection  The name of grandpa is Mark Henry and he resides in the variable name1   Scenario 2  With reflection Printing members the  reflect  way   The name of grandpa is Mark Henry and he resides in the variable name1 The name of grandpa is John Clash and he resides in the variable name2 The name of grandpa is Will Jones and he resides in the variable name3     Common Misconceptions   Please do not confuse with the below example  As you can still see  the private and protected members cannot be accessed outside of the class without using reflection   lt  php  class GrandPas      The Grandfather s class       public      name1    Mark Henry       This grandpa is mapped to a public modifier     protected   name2    John Clash       This grandpa is mapped to a protected modifier     private     name3    Will Jones       This grandpa is mapped to a private modifier     granpaWithoutReflections   new GrandPas  print r  granpaWithoutReflections     Output   GrandPas Object        name1    gt  Mark Henry      name2 protected    gt  John Clash      name3 GrandPas private    gt  Will Jones     Debugging functions  print r  var export and var dump are debugger functions  They present information about a variable in a human-readable form  These three functions will reveal the protected and private properties of objects with PHP 5  Static class members will not be shown     More resources    The PHP Manual - OOP Properties The PHP Manual - OOP Visibility Techflirt com - Visibility in PHP Classes Jordizle com - Public  Private  Protected in PHP 5

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When we follow object oriented php in our project   we should follow some rules to use access modifiers in php  Today we are going to learn clearly what is access modifier and how can we use it PHP access modifiers are used to set access rights with PHP classes and their members that are the functions and variables defined within the class scope  In php there are three scopes for class members    PUBLIC PRIVATE PROTECTED   Now  let us have a look at the following image to understand access modifier access level   Now  let us have a look at the following list to know about the possible PHP keywords used as access modifiers   public  - class or its members defined with this access modifier will be publicly accessible from anywhere  even from outside the scope of the class   private  - class members with this keyword will be accessed within the class itself  we can   t access private data from subclass  It protects members from outside class access   protected  - same as private  except by allowing subclasses to access protected superclass members   Now see the table to understand access modifier Read full article php access modifire

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They re there to allow for different levels of encapsulation

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For me  this is the most useful way to understand the three property types   Public  Use this when you are OK with this variable being directly accessed and changed from anywhere in your code    Example usage from outside of the class    myObject   new MyObject    myObject- gt publicVar    newvalue    pubVar    myObject- gt publicVar    Protected  Use this when you want to force other programmers  and yourself  to use getters setters outside of the class when accessing and setting variables  but you should be consistent and use the getters and setters inside the class as well   This or private tend to be the default way you should set up all class properties    Why  Because if you decide at some point in the future  maybe even in like 5 minutes  that you want to manipulate the value that is returned for that property or do something with it before getting setting  you can do that without refactoring everywhere you have used it in your project   Example usage from outside of the class    myObject   new MyObject    myObject- gt setProtectedVar  newvalue     protectedVar    myObject- gt getProtectedVar      Private  private properties are very similar to protected properties  But the distinguishing feature difference is that making it private also makes it inaccessible to child classes without using the parent class s getter or setter    So basically  if you are using getters and setters for a property  or if it is used only internally by the parent class and it isn t meant to be accessible anywhere else  you might as well make it private  just to prevent anyone from trying to use it directly and introducing bugs   Example usage inside a child class  that extends MyObject     this- gt setPrivateVar  newvalue     privateVar    this- gt getPrivateVar

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Public  is a default state when you declare a variable or method  can be accessed by anything directly to the object   Protected  Can be accessed only within the object and subclasses   Private  Can be referenced only within the object  not subclasses

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PHP manual has a good read on the question here       The visibility of a property or method can be defined by prefixing the declaration with the keywords public  protected or private  Class members declared public can be accessed everywhere  Members declared protected can be accessed only within the class itself and by inherited and parent classes  Members declared as private may only be accessed by the class that defines the member

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Define MyClass     class MyClass       public  public    Public       protected  protected    Protected       private  private    Private        function printHello                 echo  this- gt public          echo  this- gt protected          echo  this- gt private            obj   new MyClass    echo  obj- gt public     Works echo  obj- gt protected     Fatal Error echo  obj- gt private     Fatal Error  obj- gt printHello       Shows Public  Protected and Private          Define MyClass2     class MyClass2 extends MyClass          We can redeclare the public and protected method  but not private     protected  protected    Protected2        function printHello                 echo  this- gt public          echo  this- gt protected          echo  this- gt private            obj2   new MyClass2    echo  obj2- gt public     Works echo  obj2- gt private     Undefined echo  obj2- gt protected     Fatal Error  obj2- gt printHello       Shows Public  Protected2  Undefined   Extracted From    http   php net manual en language oop5 visibility php

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private - can be accessed from WITHIN the class only  protected - can be accessed from WITHIN the class and INHERITING classes  public - can be accessed from code OUTSIDE the class as well  This applies to functions as well as variables

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The mentioned keywords are access modifiers and help us implement Encapsulation  or information hiding   They tell the compiler which other classes should have access to the field or method being defined   private - Only the current class will have access to the field or method   protected - Only the current class and subclasses  and sometimes also same-package classes  of this class will have access to the field or method   public - Any class can refer to the field or call the method

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The difference is as follows   Public    A public variable or method can be accessed directly by any user of the class   Protected    A protected variable or method cannot be accessed by users of the class but can be accessed inside a subclass that inherits from the class   Private    A private variable or method can only be accessed internally from the class in which it is defined This means that a private variable or method cannot be called from a child that extends the class

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Considering  when   I tend to declare everything as private initially  if I m not exactly sure  Reason being  that it s usually much easier to turn a private method public than the other way round  That s because you can at least be sure that the private method hasn t been used anywhere but in the class itself  A public method may already be in use everywhere  possibly requiring an extensive re-write   Update  i go for a default of protected nowadays  because I ve come to find that it s good enough for encapsulation and doesn t get in the way when I m extending classes  which i try to avoid anyway   Only if i have a good reason to use the other two  i will   A good reason for a private method would be one that implements something inherent to that object that even an extending class should not change  factual reason  in addition to encapsulation  like internal state management   Eventually  it s still easy enough to track down where a protected method is being used usually  so i default to protected nowadays  Maybe not 100  objective  in the trenches  experience  I admit

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Here is an easy way to remember the scope of public  protected and private    PUBLIC    public scope  A public variable function is available to both objects and other classes    PROTECTED    protected scope  A protected variable function is available to all the classes that extend the current class   No  Objects cannot access this scope   PRIVATE    private scope  A private variable function is only visible in the current class where it is being defined  No  Class that extend the current class cannot access this scope  No  Objects cannot access this scope    Read the Visibility of a method or variable on PHP Manual

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Reviving an old question  but I think a really good way to think of this is in terms of the API that you are defining    public - Everything marked public is part of the API that anyone using your class interface other will use and rely on  protected - Don t be fooled  this is also part of the API  People can subclass  extend your code and use anything marked protected  private - Private properties and methods can be changed as much as you like  No one else can use these  These are the only things you can change without making breaking changes    Or in Semver terms    Changes to anything public or protected should be considered MAJOR changes   Anything new public or protected should be  at least  MINOR Only new changes to anything private can be PATCH   So in terms of maintaining code  its good to be careful about what things you make public or protected because these are the things you are promising to your users

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Variables in PHP are cast in three different type   Public   values of this variable types are available in all scope and call on execution of you code  declare as  public  examTimeTable   Private   Values of this type of variable are only available on only to the class it belongs to   private  classRoomComputers   Protected  Values of this class only and only available when Access been granted in a form of inheritance or their child class  generally used    to grant access by parent class  protected  familyWealth

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It is typically considered good practice to default to the lowest visibility required as this promotes data encapsulation and good interface design  When considering member variable and method visibility think about the role the member plays in the interaction with other objects   If you  code to an interface rather than implementation  then it s usually pretty straightforward to make visibility decisions  In general  variables should be private or protected unless you have a good reason to expose them  Use public accessors  getters setters  instead to limit and regulate access to a class s internals   To use a car as an analogy  things like speed  gear  and direction would be private instance variables  You don t want the driver to directly manipulate things like air fuel ratio  Instead  you expose a limited number of actions as public methods  The interface to a car might include methods such as accelerate    deccelerate   brake    setGear    turnLeft    turnRight    etc   The driver doesn t know nor should he care how these actions are implemented by the car s internals  and exposing that functionality could be dangerous to the driver and others on the road  Hence the good practice of designing a public interface and encapsulating the data behind that interface   This approach also allows you to alter and improve the implementation of the public methods in your class without breaking the interface s contract with client code  For example  you could improve the accelerate   method to be more fuel efficient  yet the usage of that method would remain the same  client code would require no changes but still reap the benefits of your efficiency improvement   Edit  Since it seems you are still in the midst of learning object oriented concepts  which are much more difficult to master than any language s syntax   I highly recommend picking up a copy of PHP Objects  Patterns  and Practice by Matt Zandstra  This is the book that first taught me how to use OOP effectively  rather than just teaching me the syntax  I had learned the syntax years beforehand  but that was useless without understanding the  why  of OOP

[php] What is the difference between public, private, and protected?

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