What is the difference between public protected package-private and private in Java

Question

In Java  are there clear rules on when to use each of access modifiers  namely the default  package private   public  protected and private  while making class and interface and dealing with inheritance

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Private   Methods Variables and Constructors   Methods  Variables and Constructors that are declared private can only be accessed within the declared class itself    Class and Interface   Private access modifier is the most restrictive access level  Class and interfaces cannot be private   Note  Variables that are declared private can be accessed outside the class if public getter methods are present in the class  Variables  methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members  class    Protected   Class and Interface   The protected access modifier cannot be applied to class and interfaces   Methods  fields can be declared protected  however methods and fields in a interface cannot be declared protected   Note  Protected access gives the subclass a chance to use the helper method or variable  while preventing a nonrelated class from trying to use it     Public  A class  method  constructor  interface etc declared public can be accessed from any other class    Therefore fields  methods  blocks declared inside a public class can be accessed from any class belonging to the Java Universe    Different Packages   However if the public class we are trying to access is in a different package  then the public class still need to be imported   Because of class inheritance  all public methods and variables of a class are inherited by its subclasses     Default -No keyword   Default access modifier means we do not explicitly declare an access modifier for a class  field  method  etc    Within the same Packages   A variable or method declared without any access control modifier is available to any other class in the same package  The fields in an interface are implicitly public static final and the methods in an interface are by default public   Note  We cannot Override the Static fields if you try to override it does not show any error  but it doesnot work what we except   Related Answers   Overriding static methods in java   References links  http   docs oracle com javase tutorial java javaOO accesscontrol html http   www tutorialspoint com java java access modifiers htm

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Easy rule  Start with declaring everything private  And then progress towards the public as the needs arise and design warrants it   When exposing members ask yourself if you are exposing representation choices or abstraction choices  The first is something you want to avoid as it will introduce too many dependencies on the actual representation rather than on its observable behavior   As a general rule I try to avoid overriding method implementations by subclassing  it s too easy to screw up the logic  Declare abstract protected methods if you intend for it to be overridden   Also  use the  Override annotation when overriding to keep things from breaking when you refactor

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public  If a class member is declared with public then it can be accessed from anywhere protected  If a class member is declared with keyword protected then it can be accessed from same class members  outside class members within the same package and inherited class members  If a class member is protected then it can NOT be accessed from outside package class unless the outside packaged class is inherited i e  extends the other package superclass  But a protected class member is always available to same package classes it does NOT matter weather the same package class is inherited or NOT default  In Java default is NOT an access modifier keyword  If a class member is declared without any access modifier keyword then in this case it is considered as default member  The default class member is always available to same package class members  But outside package class member can NOT access default class members even if outside classes are subclasses unlike protected members private  If a class member is declared with keyword protected then in this case it is available ONLY to same class members

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The most misunderstood access modifier in Java is protected  We know that it s similar to the default modifier with one exception in which subclasses can see it  But how  Here is an example which hopefully clarifies the confusion    Assume that we have 2 classes  Father and Son  each in its own package   package fatherpackage   public class Father       -------------------------------------------  package sonpackage   public class Son extends Father       Let s add a protected method foo   to Father   package fatherpackage   public class Father       protected void foo        The method foo   can be called in 4 contexts    Inside a class that is located in the same package where foo   is defined  fatherpackage    package fatherpackage   public class SomeClass       public void someMethod Father f  Son s                f foo            s foo             Inside a subclass  on the current instance via this or super   package sonpackage   public class Son extends Father       public void sonMethod                 this foo            super foo             On an reference whose type is the same class   package fatherpackage   public class Father       public void fatherMethod Father f                f foo       valid even if foo   is private          -------------------------------------------  package sonpackage   public class Son extends Father       public void sonMethod Son s                s foo             On an reference whose type is the parent class and it is inside the package where foo   is defined  fatherpackage   This can be included inside context no  1    package fatherpackage   public class Son extends Father       public void sonMethod Father f                f foo              The following situations are not valid    On an reference whose type is the parent class and it is outside the package where foo   is defined  fatherpackage    package sonpackage   public class Son extends Father       public void sonMethod Father f                f foo       compilation error          A non-subclass inside a package of a subclass  A subclass inherits the protected members from its parent  and it makes them private to non-subclasses    package sonpackage   public class SomeClass       public void someMethod Son s  throws Exception               s foo       compilation error

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Public Protected Default and private are access modifiers   They are meant for encapsulation  or hiding and showing contents of the class    Class can be public or default Class members can be public  protected  default or private    Private is not accessible outside the class Default is accessible only in the package  Protected in package as well as any class which extends it  Public is open for all   Normally  member variables are defined private  but member methods are public

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Access modifiers in Java  Java access modifiers are used to provide access control in Java  1  Default  Accessible to the classes in the same package only  For example     Saved in file A java package pack   class A    void msg   System out println  quot Hello quot           Saved in file B java package mypack  import pack     class B    public static void main String args        A obj   new A       Compile Time Error    obj msg       Compile Time Error        This access is more restricted than public and protected  but less restricted than private  2  Public Can be accessed from anywhere   Global Access  For example     Saved in file A java  package pack  public class A    public void msg   System out println  quot Hello quot           Saved in file B java  package mypack  import pack     class B    public static void main String args         A obj   new A        obj msg            Output Hello  3  Private Accessible only inside the same class  If you try to access private members on one class in another will throw compile error  For example  class A    private int data   40    private void msg   System out println  quot Hello java quot        public class Simple    public static void main String args         A obj   new A        System out println obj data      Compile Time Error     obj msg       Compile Time Error        4  Protected Accessible only to the classes in the same package and to the subclasses For example     Saved in file A java package pack  public class A    protected void msg   System out println  quot Hello quot           Saved in file B java package mypack  import pack     class B extends A    public static void main String args         B obj   new B        obj msg            Output  Hello

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Private   Methods Variables and Constructors   Methods  Variables and Constructors that are declared private can only be accessed within the declared class itself    Class and Interface   Private access modifier is the most restrictive access level  Class and interfaces cannot be private   Note  Variables that are declared private can be accessed outside the class if public getter methods are present in the class  Variables  methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members  class    Protected   Class and Interface   The protected access modifier cannot be applied to class and interfaces   Methods  fields can be declared protected  however methods and fields in a interface cannot be declared protected   Note  Protected access gives the subclass a chance to use the helper method or variable  while preventing a nonrelated class from trying to use it     Public  A class  method  constructor  interface etc declared public can be accessed from any other class    Therefore fields  methods  blocks declared inside a public class can be accessed from any class belonging to the Java Universe    Different Packages   However if the public class we are trying to access is in a different package  then the public class still need to be imported   Because of class inheritance  all public methods and variables of a class are inherited by its subclasses     Default -No keyword   Default access modifier means we do not explicitly declare an access modifier for a class  field  method  etc    Within the same Packages   A variable or method declared without any access control modifier is available to any other class in the same package  The fields in an interface are implicitly public static final and the methods in an interface are by default public   Note  We cannot Override the Static fields if you try to override it does not show any error  but it doesnot work what we except   Related Answers   Overriding static methods in java   References links  http   docs oracle com javase tutorial java javaOO accesscontrol html http   www tutorialspoint com java java access modifiers htm

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Caveat   I am not a Java programmer  I am a Perl programmer   Perl has no formal protections which is perhaps why I understand the problem so well       Private  Like you d think  only the class in which it is declared can see it   Package Private  It can only be seen and used by the package in which it was declared   This is the default in Java  which some see as a mistake    Protected  Package Private   can be seen by subclasses or package members   Public  Everyone can see it   Published  Visible outside the code I control    While not Java syntax  it is important for this discussion    C   defines an additional level called  friend  and the less you know about that the better   When should you use what   The whole idea is encapsulation to hide information   As much as possible you want to hide the detail of how something is done from your users   Why   Because then you can change them later and not break anybody s code   This lets you optimize  refactor  redesign  and fix bugs without worry that someone was using that code you just overhauled   So  the rule of thumb is to make things only as visible as they have to be   Start with private and only add more visibility as needed   Only make public that which is absolutely necessary for the user to know  every detail you make public cramps your ability to redesign the system   If you want users to be able to customize behaviors  rather than making internals public so they can override them  it s often a better idea to shove those guts into an object and make that interface public   That way they can simply plug in a new object   For example  if you were writing a CD player and wanted the  go find info about this CD  bit customizable  rather than make those methods public you d put all that functionality into its own object and make just your object getter setter public   In this way being stingy about exposing your guts encourages good composition and separation of concerns  Personally  I stick with just  private  and  public    Many OO languages just have that    Protected  can be handy  but it s really a cheat   Once an interface is more than private it s outside of your control and you have to go looking in other people s code to find uses   This is where the idea of  published  comes in   Changing an interface  refactoring it  requires that you find all the code which is using it and change that  too   If the interface is private  well no problem   If it s protected you have to go find all your subclasses   If it s public you have to go find all the code which uses your code   Sometimes this is possible  for example  if you re working on corporate code that s for internal use only it doesn t matter if an interface is public   You can grab all the code out of the corporate repository   But if an interface is  published   if there is code using it outside your control  then you re hosed   You must support that interface or risk breaking code   Even protected interfaces can be considered published  which is why I don t bother with protected    Many languages find the hierarchical nature of public protected private to be too limiting and not in line with reality   To that end  there is the concept of a trait class  but that s another show

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This image will make you understand easily about the basic differences between public  private  protected and default access modifiers  The default modifier takes place automatically when you don t declare ant access modifiers in your code

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In very short   public  accessible from everywhere   protected  accessible by the classes of the same package and the subclasses residing in any package  default  no modifier specified   accessible by the classes of the same package  private  accessible within the same class only

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Access modifiers in Java  Java access modifiers are used to provide access control in Java  1  Default  Accessible to the classes in the same package only  For example     Saved in file A java package pack   class A    void msg   System out println  quot Hello quot           Saved in file B java package mypack  import pack     class B    public static void main String args        A obj   new A       Compile Time Error    obj msg       Compile Time Error        This access is more restricted than public and protected  but less restricted than private  2  Public Can be accessed from anywhere   Global Access  For example     Saved in file A java  package pack  public class A    public void msg   System out println  quot Hello quot           Saved in file B java  package mypack  import pack     class B    public static void main String args         A obj   new A        obj msg            Output Hello  3  Private Accessible only inside the same class  If you try to access private members on one class in another will throw compile error  For example  class A    private int data   40    private void msg   System out println  quot Hello java quot        public class Simple    public static void main String args         A obj   new A        System out println obj data      Compile Time Error     obj msg       Compile Time Error        4  Protected Accessible only to the classes in the same package and to the subclasses For example     Saved in file A java package pack  public class A    protected void msg   System out println  quot Hello quot           Saved in file B java package mypack  import pack     class B extends A    public static void main String args         B obj   new B        obj msg            Output  Hello

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public - accessible from anywhere in the application  default - accessible from package  protected - accessible from package and sub-classes in other package  as well private - accessible from its class only

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Caveat   I am not a Java programmer  I am a Perl programmer   Perl has no formal protections which is perhaps why I understand the problem so well       Private  Like you d think  only the class in which it is declared can see it   Package Private  It can only be seen and used by the package in which it was declared   This is the default in Java  which some see as a mistake    Protected  Package Private   can be seen by subclasses or package members   Public  Everyone can see it   Published  Visible outside the code I control    While not Java syntax  it is important for this discussion    C   defines an additional level called  friend  and the less you know about that the better   When should you use what   The whole idea is encapsulation to hide information   As much as possible you want to hide the detail of how something is done from your users   Why   Because then you can change them later and not break anybody s code   This lets you optimize  refactor  redesign  and fix bugs without worry that someone was using that code you just overhauled   So  the rule of thumb is to make things only as visible as they have to be   Start with private and only add more visibility as needed   Only make public that which is absolutely necessary for the user to know  every detail you make public cramps your ability to redesign the system   If you want users to be able to customize behaviors  rather than making internals public so they can override them  it s often a better idea to shove those guts into an object and make that interface public   That way they can simply plug in a new object   For example  if you were writing a CD player and wanted the  go find info about this CD  bit customizable  rather than make those methods public you d put all that functionality into its own object and make just your object getter setter public   In this way being stingy about exposing your guts encourages good composition and separation of concerns  Personally  I stick with just  private  and  public    Many OO languages just have that    Protected  can be handy  but it s really a cheat   Once an interface is more than private it s outside of your control and you have to go looking in other people s code to find uses   This is where the idea of  published  comes in   Changing an interface  refactoring it  requires that you find all the code which is using it and change that  too   If the interface is private  well no problem   If it s protected you have to go find all your subclasses   If it s public you have to go find all the code which uses your code   Sometimes this is possible  for example  if you re working on corporate code that s for internal use only it doesn t matter if an interface is public   You can grab all the code out of the corporate repository   But if an interface is  published   if there is code using it outside your control  then you re hosed   You must support that interface or risk breaking code   Even protected interfaces can be considered published  which is why I don t bother with protected    Many languages find the hierarchical nature of public protected private to be too limiting and not in line with reality   To that end  there is the concept of a trait class  but that s another show

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Access Specifiers in Java  There are 4 access specifiers in java  namely private  package-private  default   protected and public in increasing access order   Private  When you are developing some class and you want member of this class not to be exposed outside this class then you should declare it as private  private members can be accessed only in class where they are defined i e  enclosing class  private members can be accessed on  this  reference and also on other instances of class enclosing these members  but only within the definition of this class   Package-private  default   This access specifier will provide access specified by private access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  you may use default  need not be mentioned explicitly  access specifier  to expose member within class  to other classes within your  same  package  In these other classes  within same package   you can access these default members on instance of Class1  Also you can access these default members within subclasses of Class1  say Class2  on this reference or on instance of Class1 or on instance of Class2     Basically  within same package you can access default members on instance of class directly or on  this  reference in subclasses   protected  This access specifier will provide access specified by package-private access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  then you should use protected access specifier for data member within Class1 if you don t want this member to be accessed outside your package  say in package of consumer of your package i e  client who is using your APIs  in general  but you want to make an exception and allow access to this member only if client writes class say Class2 that extends Class1  So  in general  protected members will be accessible on  this  reference in derived classes i e  Class2 and also on explicit instances of Class2   Please note    You won t be able to access inherited protected member of Class1 in Class2  if you attempt to access it on explicit instance of Class1  although it is inherited in it  When you write another class Class3 within same different package that extends Class2  protected member from Class1 will be accessible on this reference and also on explicit instance of Class3  This will be true for any hierarchy that is extended i e  protected member will still be accessible on this reference or instance of extended class  Note that in Class3  if you create instance of Class2 then you will not be able to access protected member from Class1 though it is inherited    So bottom line is  protected members can be accessed in other packages  only if some class from this other package  extends class enclosing this protected member and protected member is accessed on  this  reference or explicit instances of extended class  within definition of extended class   public  This access specifier will provide access specified by protected access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  then you should use public access specifier for data member within Class1 if you want this member to be accessible in other packages on instance of Class1 created in some class of other package  Basically this access specifier should be used when you intent to expose your data member to world without any condition

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Easy rule  Start with declaring everything private  And then progress towards the public as the needs arise and design warrants it   When exposing members ask yourself if you are exposing representation choices or abstraction choices  The first is something you want to avoid as it will introduce too many dependencies on the actual representation rather than on its observable behavior   As a general rule I try to avoid overriding method implementations by subclassing  it s too easy to screw up the logic  Declare abstract protected methods if you intend for it to be overridden   Also  use the  Override annotation when overriding to keep things from breaking when you refactor

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Access modifiers are there to restrict access at several levels   Public  It is basically as simple as you can access from any class whether that is in same package or not   To access if you are in same package you can access directly  but if you are in another package then you can create an object of the class   Default  It is accessible in the same package from any of the class of package   To access you can create an object of the class  But you can not access this variable outside of the package   Protected  you can access variables in same package as well as subclass in any other package  so basically it is default   Inherited behavior   To access protected field defined in base class you can create object of child class   Private   it can be access in same class   In non-static methods you can access directly because of this reference  also in constructors but to access in static methods you need to create object of the class

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The most misunderstood access modifier in Java is protected  We know that it s similar to the default modifier with one exception in which subclasses can see it  But how  Here is an example which hopefully clarifies the confusion    Assume that we have 2 classes  Father and Son  each in its own package   package fatherpackage   public class Father       -------------------------------------------  package sonpackage   public class Son extends Father       Let s add a protected method foo   to Father   package fatherpackage   public class Father       protected void foo        The method foo   can be called in 4 contexts    Inside a class that is located in the same package where foo   is defined  fatherpackage    package fatherpackage   public class SomeClass       public void someMethod Father f  Son s                f foo            s foo             Inside a subclass  on the current instance via this or super   package sonpackage   public class Son extends Father       public void sonMethod                 this foo            super foo             On an reference whose type is the same class   package fatherpackage   public class Father       public void fatherMethod Father f                f foo       valid even if foo   is private          -------------------------------------------  package sonpackage   public class Son extends Father       public void sonMethod Son s                s foo             On an reference whose type is the parent class and it is inside the package where foo   is defined  fatherpackage   This can be included inside context no  1    package fatherpackage   public class Son extends Father       public void sonMethod Father f                f foo              The following situations are not valid    On an reference whose type is the parent class and it is outside the package where foo   is defined  fatherpackage    package sonpackage   public class Son extends Father       public void sonMethod Father f                f foo       compilation error          A non-subclass inside a package of a subclass  A subclass inherits the protected members from its parent  and it makes them private to non-subclasses    package sonpackage   public class SomeClass       public void someMethod Son s  throws Exception               s foo       compilation error

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Often times I ve realized that remembering the basic concepts of any language can made possible by creating real-world analogies  Here is my analogy for understanding access modifiers in Java   Let s assume that you re a student at a university and you have a friend who s coming to visit you over the weekend  Suppose there exists a big statue of the university s founder in the middle of the campus    When you bring him to the campus  the first thing that you and your friend sees is this statue  This means that anyone who walks in the campus can look at the statue without the university s permission  This makes the statue as PUBLIC  Next  you want to take your friend to your dorm  but for that you need to register him as a visitor  This means that he gets an access pass  which is the same as yours  to get into various buildings on campus  This would make his access card as PROTECTED  Your friend wants to login to the campus WiFi but doesn t have the any credentials to do so  The only way he can get online is if you share your login with him   Remember  every student who goes to the university also possesses these login credentials   This would make your login credentials as NO MODIFIER  Finally  your friend wants to read your progress report for the semester which is posted on the website  However  every student has their own personal login to access this section of the campus website  This would make these credentials as PRIVATE    Hope this helps

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The difference can be found in the links already provided but which one to use usually comes down to the  Principle of Least Knowledge   Only allow the least visibility that is needed

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Here s a better version of the table  that also includes a column for modules        Explanations   A private member  i  is only accessible within the same class as it is declared  A member with no access modifier  j  is only accessible within classes in the same package  A protected member  k  is accessible within all classes in the same package and within subclasses in other packages  A public member  l  is accessible to all classes  unless it resides in a module that does not export the package it is declared in       Which modifier to choose   Access modifiers is a tool to help you to prevent accidentally breaking encapsulation     Ask yourself if you intend the member to be something that s internal to the class  package  class hierarchy or not internal at all  and choose access level accordingly   Examples    A field long internalCounter should probably be private since it s mutable and an implementation detail  A class that should only be instantiated in a factory class  in the same package  should have a package restricted constructor  since it shouldn t be possible to call it directly from outside the package  An internal void beforeRender   method called right before rendering and used as a hook in subclasses should be protected  A void saveGame File dst  method which is called from the GUI code should be public        What is Encapsulation exactly

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The difference can be found in the links already provided but which one to use usually comes down to the  Principle of Least Knowledge   Only allow the least visibility that is needed

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Visible to the package  The default  No modifiers are needed   Visible to the class only  private    Visible to the world  public    Visible to the package and all subclasses  protected    Variables and methods can be declared without any modifiers that are called  Default examples   String name    john    public int age        return age      Private access modifier - private   Methods  variables and constructors that are declared private can only be accessed within the declared class itself  The private access modifier is the most restrictive access level  Class and interfaces cannot be private   Variables that are declared private can be accessed outside the class if public getter methods are present in the class   Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world   Examples   Public class Details       private String name       public void setName String n           this name   n             public String getName            return this name            Public access modifier - public   A class  method  constructor  interface  etc  declared public can be accessed from any other class  Therefore fields  methods  blocks declared inside a public class can be accessed from any class belonging to the Java universe   However  if the public class we are trying to access is in a different package  then the public class still need to be imported   Because of class inheritance  all public methods and variables of a class are inherited by its subclasses   Example   public void cal         Protected access modifier - protected   Variables  methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in another package or any class within the package of the protected members  class   The protected access modifier cannot be applied to class and interfaces  Methods  fields can be declared protected  however methods and fields in a interface cannot be declared protected   Protected access gives the subclass a chance to use the helper method or variable  while preventing a nonrelated class from trying to use it   class Van       protected boolean speed              class Car      boolean speed

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In very short   public  accessible from everywhere   protected  accessible by the classes of the same package and the subclasses residing in any package  default  no modifier specified   accessible by the classes of the same package  private  accessible within the same class only

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It is all about encapsulation  or as Joe Phillips stated  least knowledge    Start with the most restrictive  private  and see if you need less restrictive modifiers later on   We all use method and member modifiers like private  public      but one thing too few developers do is use packages to organize code logically   For example  You may put sensitive security methods in a  security  package  Then put a public class which accesses some of the security related code in this package but keep other security classes package private  Thus other developers will only be able to use the publicly available class from outside of this package  unless they change the modifier   This is not a security feature  but will guide usage   Outside world - gt  Package  SecurityEntryClass --- gt  Package private classes    Another thing is that classes which depend a lot on each other may end up in the same package and could eventually be refactored or merged if the dependency is too strong   If on the contrary you set everything as public it will not be clear what should or should not be accessed  which may lead to writing a lot of javadoc  which does not enforce anything via the compiler

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Private  Limited access to class only  Default  no modifier   Limited access to class and package  Protected  Limited access to class  package and subclasses  both inside and outside package   Public  Accessible to class  package  all   and subclasses    In short  everywhere

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It is all about encapsulation  or as Joe Phillips stated  least knowledge    Start with the most restrictive  private  and see if you need less restrictive modifiers later on   We all use method and member modifiers like private  public      but one thing too few developers do is use packages to organize code logically   For example  You may put sensitive security methods in a  security  package  Then put a public class which accesses some of the security related code in this package but keep other security classes package private  Thus other developers will only be able to use the publicly available class from outside of this package  unless they change the modifier   This is not a security feature  but will guide usage   Outside world - gt  Package  SecurityEntryClass --- gt  Package private classes    Another thing is that classes which depend a lot on each other may end up in the same package and could eventually be refactored or merged if the dependency is too strong   If on the contrary you set everything as public it will not be clear what should or should not be accessed  which may lead to writing a lot of javadoc  which does not enforce anything via the compiler

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The official tutorial may be of some use to you        Class Package Subclass same pkg  Subclass diff pkg  World     public             protected            no modifier           private               accessible blank   not accessible

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Here s a better version of the table  that also includes a column for modules        Explanations   A private member  i  is only accessible within the same class as it is declared  A member with no access modifier  j  is only accessible within classes in the same package  A protected member  k  is accessible within all classes in the same package and within subclasses in other packages  A public member  l  is accessible to all classes  unless it resides in a module that does not export the package it is declared in       Which modifier to choose   Access modifiers is a tool to help you to prevent accidentally breaking encapsulation     Ask yourself if you intend the member to be something that s internal to the class  package  class hierarchy or not internal at all  and choose access level accordingly   Examples    A field long internalCounter should probably be private since it s mutable and an implementation detail  A class that should only be instantiated in a factory class  in the same package  should have a package restricted constructor  since it shouldn t be possible to call it directly from outside the package  An internal void beforeRender   method called right before rendering and used as a hook in subclasses should be protected  A void saveGame File dst  method which is called from the GUI code should be public        What is Encapsulation exactly

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David s answer provides the meaning of each access modifier  As for when to use each  I d suggest making public all classes and the methods of each class that are meant for external use  its API   and everything else private   Over time you ll develop a sense for when to make some classes package-private and when to declare certain methods protected for use in subclasses

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public  If a class member is declared with public then it can be accessed from anywhere protected  If a class member is declared with keyword protected then it can be accessed from same class members  outside class members within the same package and inherited class members  If a class member is protected then it can NOT be accessed from outside package class unless the outside packaged class is inherited i e  extends the other package superclass  But a protected class member is always available to same package classes it does NOT matter weather the same package class is inherited or NOT default  In Java default is NOT an access modifier keyword  If a class member is declared without any access modifier keyword then in this case it is considered as default member  The default class member is always available to same package class members  But outside package class member can NOT access default class members even if outside classes are subclasses unlike protected members private  If a class member is declared with keyword protected then in this case it is available ONLY to same class members

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Java access modifies which you can use  Access modifier can be applicable for class  field About   method  Try to access  subclass or override this   Access to field or method is through a class  Inheritance and Open Closed Principle   Successor class subclass  access modifier can be any  Successor method override  access modifier should be the same or expand it    Top level class first level scope  can be public and default  Nested class About  can have any of them package is not applying for package hierarchy  Swift access modifiers

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Easy rule  Start with declaring everything private  And then progress towards the public as the needs arise and design warrants it   When exposing members ask yourself if you are exposing representation choices or abstraction choices  The first is something you want to avoid as it will introduce too many dependencies on the actual representation rather than on its observable behavior   As a general rule I try to avoid overriding method implementations by subclassing  it s too easy to screw up the logic  Declare abstract protected methods if you intend for it to be overridden   Also  use the  Override annotation when overriding to keep things from breaking when you refactor

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Private  Limited access to class only  Default  no modifier   Limited access to class and package  Protected  Limited access to class  package and subclasses  both inside and outside package   Public  Accessible to class  package  all   and subclasses    In short  everywhere

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The official tutorial may be of some use to you        Class Package Subclass same pkg  Subclass diff pkg  World     public             protected            no modifier           private               accessible blank   not accessible

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David s answer provides the meaning of each access modifier  As for when to use each  I d suggest making public all classes and the methods of each class that are meant for external use  its API   and everything else private   Over time you ll develop a sense for when to make some classes package-private and when to declare certain methods protected for use in subclasses

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highest precedence  lt --------- gt  lowest precedence                                                                                                                                                                                                       xCanBeSeenBy   this            any class   this subclass   any                   class           in same     in another      class                   nonsubbed       package     package             Modifier of x                                                                                                                                                                                                                                                             public                                                                                                                                                                                                                                                                   protected                                                                                                                                                                                                                                                                 package-private                                                no modifier                                                                                                                                                                                                                                                              private

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Easy rule  Start with declaring everything private  And then progress towards the public as the needs arise and design warrants it   When exposing members ask yourself if you are exposing representation choices or abstraction choices  The first is something you want to avoid as it will introduce too many dependencies on the actual representation rather than on its observable behavior   As a general rule I try to avoid overriding method implementations by subclassing  it s too easy to screw up the logic  Declare abstract protected methods if you intend for it to be overridden   Also  use the  Override annotation when overriding to keep things from breaking when you refactor

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When you are thinking of access modifiers just think of it in this way  applies to both variables and methods    public --  accessible from every where private --  accessible only within the same class where it is declared  Now the confusion arises when it comes to default and protected  default --  No access modifier keyword is present  This means it is available strictly within the package of the class  Nowhere outside that package it can be accessed   protected --  Slightly less stricter than default and apart from the same package classes it can be accessed by sub classes outside the package it is declared

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My two cents     private   class -  a top level class cannot be private  inner classes can be private which are accessible from same class   instance variable -  accessible only in the class  Cannot access outside the class   package-private   class -  a top level class can be package-private  It can only be accessible from same package  Not from sub package  not from outside package   instance variable -  accessible from same package  Not from sub package  not from outside package   protected   class -  a top level class cannot be protected   instance variable -  Only accessible in same package or subpackage  Can only be access outside the package while extending class   public   class -  accessible from package subpackage another package  instance variable -  accessible from package subpackage another package  Here is detailed answer  https   github com junto06 java-4-beginners blob master basics access-modifier md

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As a rule of thumb     private  class scope  default  or package-private   package scope  protected  package scope   child  like package  but we can subclass it from different packages   The protected modifier always keeps the  parent-child  relationship  public  everywhere    As a result  if we divide access right into three rights      D irect  invoke from a method inside the same class  or via  this  syntax    R eference  invoke a method using a reference to the class  or via  dot  syntax    I nheritance  via subclassing     then we have this simple table       -                                                                                                                                             Same      Different                         Package    Packages                                                                                                                                   private             D                                                                                                                                                     package-private                               no modifier        D R I                                                                                                                                                 protected           D R I            I                                                                                                                                    public              D R I         R  I

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David s answer provides the meaning of each access modifier  As for when to use each  I d suggest making public all classes and the methods of each class that are meant for external use  its API   and everything else private   Over time you ll develop a sense for when to make some classes package-private and when to declare certain methods protected for use in subclasses

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Public Protected Default and private are access modifiers   They are meant for encapsulation  or hiding and showing contents of the class    Class can be public or default Class members can be public  protected  default or private    Private is not accessible outside the class Default is accessible only in the package  Protected in package as well as any class which extends it  Public is open for all   Normally  member variables are defined private  but member methods are public

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The difference can be found in the links already provided but which one to use usually comes down to the  Principle of Least Knowledge   Only allow the least visibility that is needed

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My two cents     private   class -  a top level class cannot be private  inner classes can be private which are accessible from same class   instance variable -  accessible only in the class  Cannot access outside the class   package-private   class -  a top level class can be package-private  It can only be accessible from same package  Not from sub package  not from outside package   instance variable -  accessible from same package  Not from sub package  not from outside package   protected   class -  a top level class cannot be protected   instance variable -  Only accessible in same package or subpackage  Can only be access outside the package while extending class   public   class -  accessible from package subpackage another package  instance variable -  accessible from package subpackage another package  Here is detailed answer  https   github com junto06 java-4-beginners blob master basics access-modifier md

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Note  This is just a supplement for the accepted answer   This is related to Java Access Modifiers   From Java Access Modifiers        A Java access modifier specifies which classes can access a given   class and its fields  constructors and methods  Access modifiers can   be specified separately for a class  its constructors  fields and   methods  Java access modifiers are also sometimes referred to in daily   speech as Java access specifiers  but the correct name is Java access   modifiers  Classes  fields  constructors and methods can have one of   four different Java access modifiers          List item   private   default  package    protected   public      From Controlling Access to Members of a Class tutorials      Access level modifiers determine whether other classes can use a   particular field or invoke a particular method  There are two levels   of access control          At the top level   public  or package-private  no explicit modifier     At the member level   public  private  protected  or package-private  no explicit modifier             A class may be declared with the modifier public  in which case that   class is visible to all classes everywhere  If a class has no modifier    the default  also known as package-private   it is visible only   within its own package      The following table shows the access to members permitted by each   modifier    --------------------------------------------------     Modifier       Class    Package    Subclass    World      ------------- ------- --------- ---------- -------      public         Y        Y          Y           Y           protected      Y        Y          Y           N           no modifier    Y        Y          N           N           private        Y        N          N           N         --------------------------------------------------        The first data column indicates whether the class itself has access to   the member defined by the access level  As you can see  a class always   has access to its own members  The second column indicates whether   classes in the same package as the class  regardless of their   parentage  have access to the member  The third column indicates   whether subclasses of the class declared outside this package have   access to the member  The fourth column indicates whether all classes   have access to the member       Access levels affect you in two ways  First  when you use classes that   come from another source  such as the classes in the Java platform    access levels determine which members of those classes your own   classes can use  Second  when you write a class  you need to decide   what access level every member variable and every method in your class   should have

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The official tutorial may be of some use to you        Class Package Subclass same pkg  Subclass diff pkg  World     public             protected            no modifier           private               accessible blank   not accessible

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This page writes well about the protected  amp  default access modifier       Protected  Protected access modifier is the a little tricky and you can say is a superset of the default access modifier  Protected members are same as the default members as far as the access in the same package is concerned  The difference is that  the protected members are also accessible to the subclasses of the class in which the member is declared which are outside the package in which the parent class is present   But these protected members are    accessible outside the package only through inheritance     i e you can access a protected member of a class in its subclass present in some other package directly as if the member is present in the subclass itself  But that protected member will not be accessible in the subclass outside the package by using parent class   s reference

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David s answer provides the meaning of each access modifier  As for when to use each  I d suggest making public all classes and the methods of each class that are meant for external use  its API   and everything else private   Over time you ll develop a sense for when to make some classes package-private and when to declare certain methods protected for use in subclasses

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Following block diagram explain how data members of base class are inherited when derived class access mode is private     Note  Declaring data members with private access specifier is known as data hiding   Source    Access Specifiers     Private  Public and Protected

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Following block diagram explain how data members of base class are inherited when derived class access mode is private     Note  Declaring data members with private access specifier is known as data hiding   Source    Access Specifiers     Private  Public and Protected

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As a rule of thumb     private  class scope  default  or package-private   package scope  protected  package scope   child  like package  but we can subclass it from different packages   The protected modifier always keeps the  parent-child  relationship  public  everywhere    As a result  if we divide access right into three rights      D irect  invoke from a method inside the same class  or via  this  syntax    R eference  invoke a method using a reference to the class  or via  dot  syntax    I nheritance  via subclassing     then we have this simple table       -                                                                                                                                             Same      Different                         Package    Packages                                                                                                                                   private             D                                                                                                                                                     package-private                               no modifier        D R I                                                                                                                                                 protected           D R I            I                                                                                                                                    public              D R I         R  I

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This image will make you understand easily about the basic differences between public  private  protected and default access modifiers  The default modifier takes place automatically when you don t declare ant access modifiers in your code

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When you are thinking of access modifiers just think of it in this way  applies to both variables and methods    public --  accessible from every where private --  accessible only within the same class where it is declared  Now the confusion arises when it comes to default and protected  default --  No access modifier keyword is present  This means it is available strictly within the package of the class  Nowhere outside that package it can be accessed   protected --  Slightly less stricter than default and apart from the same package classes it can be accessed by sub classes outside the package it is declared

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highest precedence  lt --------- gt  lowest precedence                                                                                                                                                                                                       xCanBeSeenBy   this            any class   this subclass   any                   class           in same     in another      class                   nonsubbed       package     package             Modifier of x                                                                                                                                                                                                                                                             public                                                                                                                                                                                                                                                                   protected                                                                                                                                                                                                                                                                 package-private                                                no modifier                                                                                                                                                                                                                                                              private

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Access Specifiers in Java  There are 4 access specifiers in java  namely private  package-private  default   protected and public in increasing access order   Private  When you are developing some class and you want member of this class not to be exposed outside this class then you should declare it as private  private members can be accessed only in class where they are defined i e  enclosing class  private members can be accessed on  this  reference and also on other instances of class enclosing these members  but only within the definition of this class   Package-private  default   This access specifier will provide access specified by private access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  you may use default  need not be mentioned explicitly  access specifier  to expose member within class  to other classes within your  same  package  In these other classes  within same package   you can access these default members on instance of Class1  Also you can access these default members within subclasses of Class1  say Class2  on this reference or on instance of Class1 or on instance of Class2     Basically  within same package you can access default members on instance of class directly or on  this  reference in subclasses   protected  This access specifier will provide access specified by package-private access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  then you should use protected access specifier for data member within Class1 if you don t want this member to be accessed outside your package  say in package of consumer of your package i e  client who is using your APIs  in general  but you want to make an exception and allow access to this member only if client writes class say Class2 that extends Class1  So  in general  protected members will be accessible on  this  reference in derived classes i e  Class2 and also on explicit instances of Class2   Please note    You won t be able to access inherited protected member of Class1 in Class2  if you attempt to access it on explicit instance of Class1  although it is inherited in it  When you write another class Class3 within same different package that extends Class2  protected member from Class1 will be accessible on this reference and also on explicit instance of Class3  This will be true for any hierarchy that is extended i e  protected member will still be accessible on this reference or instance of extended class  Note that in Class3  if you create instance of Class2 then you will not be able to access protected member from Class1 though it is inherited    So bottom line is  protected members can be accessed in other packages  only if some class from this other package  extends class enclosing this protected member and protected member is accessed on  this  reference or explicit instances of extended class  within definition of extended class   public  This access specifier will provide access specified by protected access specifier in addition to access described below   When you are developing some package and hence some class  say Class1  within it  then you should use public access specifier for data member within Class1 if you want this member to be accessible in other packages on instance of Class1 created in some class of other package  Basically this access specifier should be used when you intent to expose your data member to world without any condition

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Visible to the package  The default  No modifiers are needed   Visible to the class only  private    Visible to the world  public    Visible to the package and all subclasses  protected    Variables and methods can be declared without any modifiers that are called  Default examples   String name    john    public int age        return age      Private access modifier - private   Methods  variables and constructors that are declared private can only be accessed within the declared class itself  The private access modifier is the most restrictive access level  Class and interfaces cannot be private   Variables that are declared private can be accessed outside the class if public getter methods are present in the class   Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world   Examples   Public class Details       private String name       public void setName String n           this name   n             public String getName            return this name            Public access modifier - public   A class  method  constructor  interface  etc  declared public can be accessed from any other class  Therefore fields  methods  blocks declared inside a public class can be accessed from any class belonging to the Java universe   However  if the public class we are trying to access is in a different package  then the public class still need to be imported   Because of class inheritance  all public methods and variables of a class are inherited by its subclasses   Example   public void cal         Protected access modifier - protected   Variables  methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in another package or any class within the package of the protected members  class   The protected access modifier cannot be applied to class and interfaces  Methods  fields can be declared protected  however methods and fields in a interface cannot be declared protected   Protected access gives the subclass a chance to use the helper method or variable  while preventing a nonrelated class from trying to use it   class Van       protected boolean speed              class Car      boolean speed

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This page writes well about the protected  amp  default access modifier       Protected  Protected access modifier is the a little tricky and you can say is a superset of the default access modifier  Protected members are same as the default members as far as the access in the same package is concerned  The difference is that  the protected members are also accessible to the subclasses of the class in which the member is declared which are outside the package in which the parent class is present   But these protected members are    accessible outside the package only through inheritance     i e you can access a protected member of a class in its subclass present in some other package directly as if the member is present in the subclass itself  But that protected member will not be accessible in the subclass outside the package by using parent class   s reference

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Caveat   I am not a Java programmer  I am a Perl programmer   Perl has no formal protections which is perhaps why I understand the problem so well       Private  Like you d think  only the class in which it is declared can see it   Package Private  It can only be seen and used by the package in which it was declared   This is the default in Java  which some see as a mistake    Protected  Package Private   can be seen by subclasses or package members   Public  Everyone can see it   Published  Visible outside the code I control    While not Java syntax  it is important for this discussion    C   defines an additional level called  friend  and the less you know about that the better   When should you use what   The whole idea is encapsulation to hide information   As much as possible you want to hide the detail of how something is done from your users   Why   Because then you can change them later and not break anybody s code   This lets you optimize  refactor  redesign  and fix bugs without worry that someone was using that code you just overhauled   So  the rule of thumb is to make things only as visible as they have to be   Start with private and only add more visibility as needed   Only make public that which is absolutely necessary for the user to know  every detail you make public cramps your ability to redesign the system   If you want users to be able to customize behaviors  rather than making internals public so they can override them  it s often a better idea to shove those guts into an object and make that interface public   That way they can simply plug in a new object   For example  if you were writing a CD player and wanted the  go find info about this CD  bit customizable  rather than make those methods public you d put all that functionality into its own object and make just your object getter setter public   In this way being stingy about exposing your guts encourages good composition and separation of concerns  Personally  I stick with just  private  and  public    Many OO languages just have that    Protected  can be handy  but it s really a cheat   Once an interface is more than private it s outside of your control and you have to go looking in other people s code to find uses   This is where the idea of  published  comes in   Changing an interface  refactoring it  requires that you find all the code which is using it and change that  too   If the interface is private  well no problem   If it s protected you have to go find all your subclasses   If it s public you have to go find all the code which uses your code   Sometimes this is possible  for example  if you re working on corporate code that s for internal use only it doesn t matter if an interface is public   You can grab all the code out of the corporate repository   But if an interface is  published   if there is code using it outside your control  then you re hosed   You must support that interface or risk breaking code   Even protected interfaces can be considered published  which is why I don t bother with protected    Many languages find the hierarchical nature of public protected private to be too limiting and not in line with reality   To that end  there is the concept of a trait class  but that s another show

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Caveat   I am not a Java programmer  I am a Perl programmer   Perl has no formal protections which is perhaps why I understand the problem so well       Private  Like you d think  only the class in which it is declared can see it   Package Private  It can only be seen and used by the package in which it was declared   This is the default in Java  which some see as a mistake    Protected  Package Private   can be seen by subclasses or package members   Public  Everyone can see it   Published  Visible outside the code I control    While not Java syntax  it is important for this discussion    C   defines an additional level called  friend  and the less you know about that the better   When should you use what   The whole idea is encapsulation to hide information   As much as possible you want to hide the detail of how something is done from your users   Why   Because then you can change them later and not break anybody s code   This lets you optimize  refactor  redesign  and fix bugs without worry that someone was using that code you just overhauled   So  the rule of thumb is to make things only as visible as they have to be   Start with private and only add more visibility as needed   Only make public that which is absolutely necessary for the user to know  every detail you make public cramps your ability to redesign the system   If you want users to be able to customize behaviors  rather than making internals public so they can override them  it s often a better idea to shove those guts into an object and make that interface public   That way they can simply plug in a new object   For example  if you were writing a CD player and wanted the  go find info about this CD  bit customizable  rather than make those methods public you d put all that functionality into its own object and make just your object getter setter public   In this way being stingy about exposing your guts encourages good composition and separation of concerns  Personally  I stick with just  private  and  public    Many OO languages just have that    Protected  can be handy  but it s really a cheat   Once an interface is more than private it s outside of your control and you have to go looking in other people s code to find uses   This is where the idea of  published  comes in   Changing an interface  refactoring it  requires that you find all the code which is using it and change that  too   If the interface is private  well no problem   If it s protected you have to go find all your subclasses   If it s public you have to go find all the code which uses your code   Sometimes this is possible  for example  if you re working on corporate code that s for internal use only it doesn t matter if an interface is public   You can grab all the code out of the corporate repository   But if an interface is  published   if there is code using it outside your control  then you re hosed   You must support that interface or risk breaking code   Even protected interfaces can be considered published  which is why I don t bother with protected    Many languages find the hierarchical nature of public protected private to be too limiting and not in line with reality   To that end  there is the concept of a trait class  but that s another show

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It s actually a bit more complicated than a simple grid shows  The grid tells you whether an access is allowed  but what exactly constitutes an access  Also  access levels interact with nested classes and inheritance in complex ways   The  default  access  specified by the absence of a keyword  is also called package-private  Exception  in an interface  no modifier means public access  modifiers other than public are forbidden  Enum constants are always public   Summary  Is an access to a member with this access specifier allowed    Member is private  Only if member is defined within the same class as calling code  Member is package private  Only if the calling code is within the member s immediately enclosing package  Member is protected  Same package  or if member is defined in a superclass of the class containing the calling code  Member is public  Yes    What access specifiers apply to  Local variables and formal parameters cannot take access specifiers  Since they are inherently inaccessible to the outside according to scoping rules  they are effectively private   For classes in the top scope  only public and package-private are permitted  This design choice is presumably because protected and private would be redundant at the package level  there is no inheritance of packages    All the access specifiers are possible on class members  constructors  methods and static member functions  nested classes    Related  Java Class Accessibility  Order  The access specifiers can be strictly ordered     public   protected   package-private   private   meaning that public provides the most access  private the least  Any reference possible on a private member is also valid for a package-private member  any reference to a package-private member is valid on a protected member  and so on   Giving access to protected members to other classes in the same package was considered a mistake    Notes   A class s methods are allowed to access private members of other objects of the same class  More precisely  a method of class C can access private members of C on objects of any subclass of C  Java doesn t support restricting access by instance  only by class   Compare with Scala  which does support it using private this    You need access to a constructor to construct an object  Thus if all constructors are private  the class can only be constructed by code living within the class  typically static factory methods or static variable initializers   Similarly for package-private or protected constructors    Only having private constructors also means that the class cannot be subclassed externally  since Java requires a subclass s constructors to implicitly or explicitly call a superclass constructor   It can  however  contain a nested class that subclasses it      Inner classes  You also have to consider nested scopes  such as inner classes  An example of the complexity is that inner classes have members  which themselves can take access modifiers  So you can have a private inner class with a public member  can the member be accessed   See below   The general rule is to look at scope and think recursively to see whether you can access each level   However  this is quite complicated  and for full details  consult the Java Language Specification   Yes  there have been compiler bugs in the past    For a taste of how these interact  consider this example  It is possible to  leak  private inner classes  this is usually a warning   class Test       public static void main final String     args            System out println Example leakPrivateClass        OK         Example leakPrivateClass   secretMethod       error          class Example       private static class NestedClass           public void secretMethod                 System out println  Hello                        public static NestedClass leakPrivateClass             return new NestedClass              Compiler output   Test java 4  secretMethod   in Example NestedClass is defined in an inaccessible class or interface         Example leakPrivateClass   secretMethod       error                                     1 error   Some related questions    Java - Method accessibility inside package-private class

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Access modifiers are there to restrict access at several levels   Public  It is basically as simple as you can access from any class whether that is in same package or not   To access if you are in same package you can access directly  but if you are in another package then you can create an object of the class   Default  It is accessible in the same package from any of the class of package   To access you can create an object of the class  But you can not access this variable outside of the package   Protected  you can access variables in same package as well as subclass in any other package  so basically it is default   Inherited behavior   To access protected field defined in base class you can create object of child class   Private   it can be access in same class   In non-static methods you can access directly because of this reference  also in constructors but to access in static methods you need to create object of the class

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Often times I ve realized that remembering the basic concepts of any language can made possible by creating real-world analogies  Here is my analogy for understanding access modifiers in Java   Let s assume that you re a student at a university and you have a friend who s coming to visit you over the weekend  Suppose there exists a big statue of the university s founder in the middle of the campus    When you bring him to the campus  the first thing that you and your friend sees is this statue  This means that anyone who walks in the campus can look at the statue without the university s permission  This makes the statue as PUBLIC  Next  you want to take your friend to your dorm  but for that you need to register him as a visitor  This means that he gets an access pass  which is the same as yours  to get into various buildings on campus  This would make his access card as PROTECTED  Your friend wants to login to the campus WiFi but doesn t have the any credentials to do so  The only way he can get online is if you share your login with him   Remember  every student who goes to the university also possesses these login credentials   This would make your login credentials as NO MODIFIER  Finally  your friend wants to read your progress report for the semester which is posted on the website  However  every student has their own personal login to access this section of the campus website  This would make these credentials as PRIVATE    Hope this helps

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public - accessible from anywhere in the application  default - accessible from package  protected - accessible from package and sub-classes in other package  as well private - accessible from its class only

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The official tutorial may be of some use to you        Class Package Subclass same pkg  Subclass diff pkg  World     public             protected            no modifier           private               accessible blank   not accessible

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Java access modifies which you can use  Access modifier can be applicable for class  field About   method  Try to access  subclass or override this   Access to field or method is through a class  Inheritance and Open Closed Principle   Successor class subclass  access modifier can be any  Successor method override  access modifier should be the same or expand it    Top level class first level scope  can be public and default  Nested class About  can have any of them package is not applying for package hierarchy  Swift access modifiers

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It s actually a bit more complicated than a simple grid shows  The grid tells you whether an access is allowed  but what exactly constitutes an access  Also  access levels interact with nested classes and inheritance in complex ways   The  default  access  specified by the absence of a keyword  is also called package-private  Exception  in an interface  no modifier means public access  modifiers other than public are forbidden  Enum constants are always public   Summary  Is an access to a member with this access specifier allowed    Member is private  Only if member is defined within the same class as calling code  Member is package private  Only if the calling code is within the member s immediately enclosing package  Member is protected  Same package  or if member is defined in a superclass of the class containing the calling code  Member is public  Yes    What access specifiers apply to  Local variables and formal parameters cannot take access specifiers  Since they are inherently inaccessible to the outside according to scoping rules  they are effectively private   For classes in the top scope  only public and package-private are permitted  This design choice is presumably because protected and private would be redundant at the package level  there is no inheritance of packages    All the access specifiers are possible on class members  constructors  methods and static member functions  nested classes    Related  Java Class Accessibility  Order  The access specifiers can be strictly ordered     public   protected   package-private   private   meaning that public provides the most access  private the least  Any reference possible on a private member is also valid for a package-private member  any reference to a package-private member is valid on a protected member  and so on   Giving access to protected members to other classes in the same package was considered a mistake    Notes   A class s methods are allowed to access private members of other objects of the same class  More precisely  a method of class C can access private members of C on objects of any subclass of C  Java doesn t support restricting access by instance  only by class   Compare with Scala  which does support it using private this    You need access to a constructor to construct an object  Thus if all constructors are private  the class can only be constructed by code living within the class  typically static factory methods or static variable initializers   Similarly for package-private or protected constructors    Only having private constructors also means that the class cannot be subclassed externally  since Java requires a subclass s constructors to implicitly or explicitly call a superclass constructor   It can  however  contain a nested class that subclasses it      Inner classes  You also have to consider nested scopes  such as inner classes  An example of the complexity is that inner classes have members  which themselves can take access modifiers  So you can have a private inner class with a public member  can the member be accessed   See below   The general rule is to look at scope and think recursively to see whether you can access each level   However  this is quite complicated  and for full details  consult the Java Language Specification   Yes  there have been compiler bugs in the past    For a taste of how these interact  consider this example  It is possible to  leak  private inner classes  this is usually a warning   class Test       public static void main final String     args            System out println Example leakPrivateClass        OK         Example leakPrivateClass   secretMethod       error          class Example       private static class NestedClass           public void secretMethod                 System out println  Hello                        public static NestedClass leakPrivateClass             return new NestedClass              Compiler output   Test java 4  secretMethod   in Example NestedClass is defined in an inaccessible class or interface         Example leakPrivateClass   secretMethod       error                                     1 error   Some related questions    Java - Method accessibility inside package-private class

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The difference can be found in the links already provided but which one to use usually comes down to the  Principle of Least Knowledge   Only allow the least visibility that is needed

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Note  This is just a supplement for the accepted answer   This is related to Java Access Modifiers   From Java Access Modifiers        A Java access modifier specifies which classes can access a given   class and its fields  constructors and methods  Access modifiers can   be specified separately for a class  its constructors  fields and   methods  Java access modifiers are also sometimes referred to in daily   speech as Java access specifiers  but the correct name is Java access   modifiers  Classes  fields  constructors and methods can have one of   four different Java access modifiers          List item   private   default  package    protected   public      From Controlling Access to Members of a Class tutorials      Access level modifiers determine whether other classes can use a   particular field or invoke a particular method  There are two levels   of access control          At the top level   public  or package-private  no explicit modifier     At the member level   public  private  protected  or package-private  no explicit modifier             A class may be declared with the modifier public  in which case that   class is visible to all classes everywhere  If a class has no modifier    the default  also known as package-private   it is visible only   within its own package      The following table shows the access to members permitted by each   modifier    --------------------------------------------------     Modifier       Class    Package    Subclass    World      ------------- ------- --------- ---------- -------      public         Y        Y          Y           Y           protected      Y        Y          Y           N           no modifier    Y        Y          N           N           private        Y        N          N           N         --------------------------------------------------        The first data column indicates whether the class itself has access to   the member defined by the access level  As you can see  a class always   has access to its own members  The second column indicates whether   classes in the same package as the class  regardless of their   parentage  have access to the member  The third column indicates   whether subclasses of the class declared outside this package have   access to the member  The fourth column indicates whether all classes   have access to the member       Access levels affect you in two ways  First  when you use classes that   come from another source  such as the classes in the Java platform    access levels determine which members of those classes your own   classes can use  Second  when you write a class  you need to decide   what access level every member variable and every method in your class   should have

[java] What is the difference between public, protected, package-private and private in Java?

Private

Protected

Public

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