In Java, is there a way to have an access modifier which is essentially private, except that this method can be accessed by children? I am developing a program in which there are several methods which are needed by the children of a certain class (and want to avoid duplication), but I don't want to make it public as I do not want the objects these childish classes are instantiated in to have access to these methods.
If there is no such thing, what would you guys recommend as to achieving best practice on this issue?
Preferably in the same package - protected doesn't fulfil this.
This is what the protected keyword is for.
https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.
Edit: Please be also aware that the Java Reflection API allows any class to access any member of your classes whatever the modifier.
Related
Is protected attribute a valid method (best pratice) to use (read and modify) variables in various classes of the same package, or is there any motivation to don't do this?
If your class isn't mean to be extended, you can also try the default modifier.
Protected allows access from all classes in the same package and from all classes that subclass your class. Default allows access only from inside the package.
Check this for more information on access modifiers.
You should also consider using getters and setters.
This is one of the main intentions of protected. The other one is for usage in sub-classes. So yes, this is a good way of doing it. But ... I would use protected (getter/setter) methods instead, if possible. Don't have the variables themselves as protected, and don't modify them directly.
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What is the difference between public, protected, package-private and private in Java?
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I have a problem understanding access modifiers in Java.
public: can be used anywhere.
private: can only be used inside the same class.
protected: can only be used in subclasses.
I saw many examples and tried but I couldn't understand.
I know only the definition. Please any one help me one this give me more examples.
What kind of programs would use private?
What kind of programs would use protected?
What kind of programs would use public?
This is very basic in OOP concepts. When the class should need to not to expose it parameters, it would define them as "private". Any class outside have no any access to it. Either these variables are for the use of the class itself only or there are public getters and setters which give indirect but controlled access to these variables.
example is age. Let say someone need to set minus value to age, then the setter method can avoid setting that value. It is a bad practice in OOP to expose variables as public. If you do that, any other logic which can create an instance of the class can change the value of the varible.
The variables are marked "protected" when we need to allow sub classes too can use or have access to these variables.
Mostly public access modifier is used for methods
You would use all three in all kinds of programs, except for very simple programs where everything is typically public.
A good practice is to use the most restrictive access modifier that you can. Access modifiers exist to help you stop yourself from making mistakes - they are not actually required per se, but they are very useful. If you're writing a library for other people to use (which you aren't, but you might in the future) they also stop other people doing weird things with your code.
Usually, a class is related to one thing (e.g. a book in a library). If you are writing a library system, you might have a class like this:
public class Book
{
private String title;
public String getTitle() {return title;}
public Book(String t) {title = t;}
...
}
Notice that title is private, so you can't directly get or set the title of a Book. You can indirectly get it using the getTitle method, which is public. You can only set it once, when the Book is created.
Code inside the Book class can still set the title, so this is not foolproof. final would be better for that, but this is to demonstrate access modifiers, not final.
You could just make title public, and say that you won't change the title of a book, but later you might do it by mistake. Again, access modifiers help you prevent yourself (and sometimes other people) making mistakes.
Edit: Also, you're wrong about protected. protected things are accessible to subclasses or classes in the same package. There's also a default access modifier, which has no keyword, which you get if you don't use public, protected or private. The default access modifier makes things accessible to the same package only.
private is used when you have variables or methods in a class which you will not use outside the class.
public is used for variables and methods which need to be accessed outside this class.
protected is used when the variables need to be used only that class and in its child class.
here is a good example.
How do I change my mistakenly c#-ish design to work with sensible access protection in java?
Here is my super class
abstract class Parent {
protected parentVariable;
protected parentMethod() {
//These methods and variables contain internal workings of my sub-classes
//to avoid repetition
// I don't want classes elsewhere in the package (that don't inherit from class) to see these.
}
}
I have sub classes that have shared internal working, which I've stuck it in the super class. It's still hidden to the other classes and usable by sub classes. Wait, no: this isn't c#, this is java.
Protected(c#) != Protected(java) ≈≈ Internal(C#).
c# protected = Access is limited to the containing class or types derived from the containing class.
java protected = Access is limited to the current package
Everything in the package can see access these. That's far too permissive for these internal workings.
How do I solve this? Do I have to bring the shared code down to the sub-classes and use "private" at the cost of code repetition? Was my use of parent classes bad design in the first place? Do I have to squirrel these inheritance trees away in new packages?
There is no access modifier that allows visibility to subclasses but not to classes of the same package.
But that's not such a big problem because classes in a given package are supposed to be "friend", cooperate, and be released all at the same time.
Even if they see some fields and methods that they shouldn't use, the other classes of the package are not part of any external API that you have no control on, and the protected methods are not accessible to the external code.
So, just document that these methods and fields shouldn't be used so that you or your coworkers don't mistakenly use them. Or put this class in its own package if you're really concerned about same-package visibility.
We have a getter method within a class.
Within the same JAR we want the variable to be accessible with the no-identifier access level, from the same package and subpackages.
Below the access levels from: http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
Our problem is, how do we stop someone from taking the compiled .JAR, creating a class with the same package namespace definition, and being able to access our variable through the getter?
We thought about getting rid of all getters for the specific variable, and giving the variable value to other classes with setters and constructors, when they pass a reference to themselves. Obviously, they will be final classes. This way all objects needing the variable value have their own private copy.
I'm wondering though if there is a better way?
Access control modifiers (public, private, protected) are not meant as a security tool, but as an OO design tool. They're used to implement OO patterns like encapsulation, inheritance.
Even with no getter whatsoever and a private variable, any Java developer can use reflection to access the variable.
If you want to keep something secret, don't ever put it in a variable of a program executed by anyone. Keep it on your own machines.
- Reflection seems to be the evil here, using which any variable even with private access modifier can be accessed.
- Four access controls like private, default, protected, and public are introduced in Java more as a tool to support the Core Object Oriented Concept like Inheritance, Encapsulation etc...
I am relatively new to java and I did some reading about private and public acccess modifiers. I would like to eliminate any confusion once and forall in this topic because I feel like I don't have the best grasp on it.
Access modifiers in variables
Please correct me if I am wrong, a variable is public on default. If the access modifier is set to public or just not set at all, than other classes from the same project can access the integer and/or modify it. If it is private than it is not visible to the outside and cannot be accessed by classes outside the one in which it was created.
Accesss modifiers in classes
Access modifiers in classes, I don't seem to fully understand. As far as my understanding, if I call a private method from method that is not in the same class, than it will not work. If it is public than it will?
Is there anything I am missing or don't understand correctly?
I appreciate help in this regard.
Please correct me if I am wrong, a variable is public on default.
You're wrong. Assuming you mean fields, by default, they have "package" access, which can't be expressed explicitly. Local variables have no concept of access control - they only exist within the context of a method anyway, so can't be referred to from anywhere else.
If the access modifier is set to public or just not set at all, than other classes from the same project can access the integer and/or modify it.
If it's set public, then any code can access it.
If it's default (package) access, then any code in the same package can access it.
Access modifiers in classes, I don't seem to fully understand. As far as my understanding, if I call a private method from method that is not in the same class, than it will not work. If it is public than it will?
That's pretty much right, yes.
I suggest you read the Java tutorial on all of this, and consult the language spec section 6.6 for more details.
Here's a good doc on the subject.
There are four access levels:
private: Only that class (not even descendants) can access.
protected: Only that class and its descendants and classes in the same package can access.
package-private (no specifier)--only classes in the same package can access--even subclasses that are not in the same package cannot.
public: Everything can access.
For for both classes member variables and methods, the default access is package private.
You can find information about the 4 modifiers here on Oracles website.
If you do not specify the modifier, it is said to be on default, which means only any code in the same package can access it.
If it's set public, then any code in any package can access it.
Actually in Java there are four different access modifiers, private, public, protected and package specific. "Please correct me if I am wrong, a variable is public on default" - you are wrong here a variable if not declared differently has a package related access. If it is set to public then it can be modified by other classes even outside of the original package. This website - http://javapapers.com/core-java/access-modifiers-in-java-explain/ - can provide you useful hints. Actually it is very easy once you read a bit more on OO concepts such as Encapsulation. Then you will understand the purpose of access modifiers (to ensure data integerity).
Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are:
Default : Visible to the package. No modifiers are needed.
Private : Visible to the class only.
Public : Visible to the world. All classes and packages.
Protected : Visible to the package and all subclasses.
If no access modifier is specified by the programmer, default access modifier is used.
Access Modifiers:
Public - {Can access anywhere in the project}
Private - {Can access only inside the class}
Protected - {Can access within the package and sub classes}
Default - {can access within the package}
Non-Access Modifiers:
Static - {for creating class variable and method}
Final - {for creating finalized class, variable and method}
Abstract - {for creating abstract method and class}
Synchronized - {for threads}
To learn more follow this link
private and public java access specifiers.in java,private access specifiers it specifies the access.private is like own family property that can uses only which family belongs.that means inside the class,method and variable can be used.
public is like government properties that means every one can access the properties without any need of tokens
private and public java access specifiers.in java,private access specifiers it specifies the access.
private is like own family property that can uses only which family
belongs.that means inside the class,method and variable can be used
.
public is like government properties that means every one can access
the properties without any need of tokens