The difference between public and protected is that public can be accessed from outside class but protected cannot be accessed from outside class. In the example above, we created a protected method inside the Addition class. Later, we extended the Test class to use the Addition class.
We can run this with no compile error. The protected method will transfer to the public class. Private access modifier only allows the data member to be accessed by class.
Class and Interface cannot be declared as private. In the example above, we are trying to create a new outside object in the inside class. When we run this code, we will get a compile-time error because the method inside-outside class is private, which means that other classes cannot access it.
It is best practice to use private access modifier when you are coding. This allows for more control of everything you are doing. In summary, we have private, public and protected access modifiers available to use in Java.
All of the access modifiers serve a different need when we code. One key thing to remember is to always try to use private if you can, next best access modifier is protected then the public is the last. 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.
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. 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:. 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:.
Inside a class that is located in the same package where foo is defined fatherpackage :. 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.
On an reference whose type is the parent class and it is outside the package where foo is defined fatherpackage :. 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 :. Methods, Variables and Constructors that are declared private can only be accessed within the declared class itself.
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. 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.
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.
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.
Default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc. 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. We cannot Override the Static fields. 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. Protected : Limited access to class, package and subclasses both inside and outside package. Public : Accessible to class, package all , and subclasses In short, everywhere. If you try to access private members on one class in another will throw compile error. For example,. 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. 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. 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.
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.
Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world. A class, method, constructor, interface, etc.
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.
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. 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.
Access modifier can be applicable for class , field [About] , method. Try to access, subclass or override this. Top level class first level scope can be public and default. Nested class [About] can have any of them. 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. 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:. 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:. 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 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. 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. 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. 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. 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. 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.
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.
When you are thinking of access modifiers just think of it in this way applies to both variables and methods :. This means it is available strictly within the package of the class.
Nowhere outside that package it can be accessed. 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. It can only be accessible from same package. Not from sub package, not from outside package. Can only be access outside the package while extending class. 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, 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. 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 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.
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. 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.
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