Overriding and Access Modifier

Is it must to override with the same access modifiers ?
For example
class A {
protected void test() {
class B extends A {
//overrides test() here
}

RZP wrote:
Is it must to override with the same access modifiers ?No, but an overridden method cannot have more restrictive access modifiers, so
public String getName();cannot be overridden by
protected String getName();However, the other way around is fine.
Winston

Similar Messages

What is the difference between access specifiers and access modifiers?

what is the difference between access specifiers and access modifiers? are they same? if not what is the difference.

Access Specifier are used to specifiy how the member variable ,methods or class to other classes.They are public ,private and protected.
Access Modifier:
1.Access
2.Non Access
Access:
public ,private,protected and default.
Non Access:
abstract,final,native,static,synchronized,transient,volatile and strictfp

Acces specifiers and Access Modifiers in java

what are Access specifiers?
what are Access modifiers?
Whether both of them are same or is there any difference?

As far as I know "access specifier" == "access modifier".
To me, they both mean "the Java Language word which specifies the visibility of a class or class attribute".
http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html
... but I'm no expert.
Cheers.

Understanding the combination of inheritance, packages and access modifiers

I am working on a problem to help my practical understanding of accessing inherited members and methods from a different package using both inheritance and instance variable.
Unfortunately, I am totally lost when I tried to set this up and understand what was happening.
Problem:
Create a class named "classA" under package "pack1" with 4 members (int pub_a, int priv_a, int prot_a, int def_a) and methods (pub_func1, priv_func1, prot_func1, def_func1). Mark the members and methods with 4 different access specifiers (public, private, protected, and default)
Create a class named "classB" under package "pack2", ClassB will inherit classA of package pack1. ClassB will have 2 members (int pub_b, int priv_b) and methods (pub_func2, prot_func2) with 2 different access specifiers (public, protected)
Try accessing the members of class classA in package pack1 inside class classB of package pack2. Find out what members and methods are accessible and not-accessible through inheritance.
Create an instance of class classA inside class classB of package pack2. Find out what members and methods are accessible and not-accessible through the instance.
Note: In your solution, comment out the lines that are in-accessible with the actual error message at the top of the comment.
So I produced the following code (I don't think i set this up right):
//filename A.java
package pack1;
public class A {
     public int pub_a;
     private int priv_a;
     protected int prot_a;
     int def_a;
     public int pub_func1() {return 1;}
     private int priv_func1() {return 2;}
     protected int prot_func1() {return 3;}
     int def_func1() {return 4;}
//filename B.java
package pack2;
import pack1.A;
public class B extends A{
     public     int pub_b;
     private int priv_b;
     public int pub_func2() { return 5; }
     private int priv_func2() { return 6; }
     //directly inherited fields, at least one should be accessible?
     pub_a = 1;
     priv_a = 1;
     prot_a = 1;
     def_a = 1;
     int i;
     // directly inherited methods, at least one should be accessible?
     i = pub_func1();
     i = priv_func2();
     A a = new A();
     //not sure what's accessible here, as no error red underlines appear
     a.pub_a = 1;
     a.priv_a = 1;
     a.prot_a = 1;
     a.def_a = 1;
}I would be interested to know how one would approach and address this problem.

//filename B.java
package pack2;
import pack1.A;
public class B extends A{
     public     int pub_b;
     private int priv_b;
     public int pub_func2() { return 5; }
     private int priv_func2() { return 6; }
     //directly inherited fields, at least one should be accessible?
     pub_a = 1;//true
     priv_a = 1;// false
     prot_a = 1;//true
     def_a = 1;//false
     int i;
     // directly inherited methods, at least one should be accessible?
     i = pub_func1();//true
     i = priv_func2();//false
     A a = new A();
     //not sure what's accessible here, as no error red underlines appear
     a.pub_a = 1;//true
     a.priv_a = 1;//false
     a.prot_a = 1//false;
     a.def_a = 1;//false
}Edited by: fun_with_me on May 31, 2008 8:30 AM

Protected and public access modifier - exact difference

Hi everybody,
Please help me to give an exact difference between protected access modifier and public
Protected: Classes with in the same package as well as subclasses can access.
Public : Classes outside the current class can access while declaring public.
My doubt is that what is the practical difference between public and protected.
I searched the net , but the information was not satisfactory to solve my confusion.
Thanks & regards
Parvathy

Obviously doubt = lacks the ability to think for
oneself.When one person raises a doubt, that does n't mean that he lacks the ability to think . He/She might have thought about it and if he didnt get a proper clarification then it will be posted in the forum.
In such cases please dont discourage others who are ready to answer the subject.Without knowing the actual intention , i request you please dont reply like this

What are Access Modifiers and Access Specifiers??

what are Access Modifiers and Access Specifiers??
advance thanks

http://www.google.com/search?q=what+are+Access+Modifiers+and+Access+Specifiers%3F
Advance welcome.
~

VLAN Override and Web Auth: How to overcome issues?

Hello
I have been investigating if we can deploy vlan override and assign a user vlan via RADIUS, post authentication on a WRD SSID. Having read around the discussions, I can see that there are others who have wanted similar, but have been told that it is not possible:
"Marucho, the particularity of how Web authentication works on the WLC is that it is carried over HTTP between Client and WLC. So the Wireless Client has to already have an IP address prior to starting the web authentication. Since the Wireless Client already has an IP address then you cannot override it anymore.
Unlike dot1x, which takes place over EAPOL and then when you have eap success, client moves to get an ip address from the sent by Radius VLAN."
However, we still have a problem that we would like to overcome and wonder if anyone has any experience or suggestions they could share?
We are a University with a large number of devices grabbing an IP address whilst only remaining associated and not actually going on to authenticate through the WRD. This creates a situation where we have a large number of IP addresses deployed unnecessarily and we would like to tackle this.
We are unable to use private IP for authenticated users (Policy decision) but could use them for associated users and so were hoping we might be able to deploy a private subnet on the WRD SSID prior to authentication and then use VLAN override to assign authenticated users onto the correct VLAN. In order to try and achieve this we were planning on using a very short DHCP lease on the private subnet, so that post-authentication the client device requests a public IP address almost instantly.
Is there any way of achieving this that someone could suggest or would we be knocking our ehads against a brick wall?
thanks
Bryn

Just giving 2 ideas :
-How about using a WPA PSK on your webauth ssid ? Just give the PSK in the SSID name. This prevents non-intended connections (no automatic association because it's open ssid) and still allows anyone with an intention, to connect to it and you still have the webauth behind. This reduces number of ip addresses.
-How about modifying the webauth successful authentication page to give the credentails to access a private network (PSK or dot1x) where credentials would regularly change ?
Those are workarounds.
Nicolas

How do I store VI References in global variables and access them later

From what I know, Labview automatically deletes VI references when they go out of use. Is there a way for me to override this so that I can access a set of preloaded references in a separate VI? Essentially I would like to open the VI's dynamically into the memory, store the references in global variables and access them at a later time. The VI's I'm referencing won't be known until runtime. I know its not the safest way to do it, but it would be the most productive on my end.
Thank you
Clay Upton

I'm not sure what you mean by "a later time", but a VI reference will remain valid as long as the VI is in memory. If you don't unload the VIs, the references will remain valid.
If you do need to unload the VIs, for whatever reason, I would suggest the following:
Create a functional global as your interface for obtaining the references.
Feed the paths to the VIs into the VI when initializing it (since you don't know which VIs in advance).
When calling the VI to obtain the references, have the VI check them first (using the Not a Number... primitive). If it sees that they're invalid, it can open a new reference and return that.
You should note that when a VI is removed from memory, the data space is used is released, so if those VIs are expected to hold data (using shift registers, etc.) this will be a problem.
The description I've given will only be usable in certain instances (and it has its intricacies), but you didn't really give any details about what you're actually trying to accomplish.
Try to take over the world!

Default/package/none access modifier

Hi,
I was hoping for some discussion on the default/package/none access modifier. It's always really bugged me that we have public, private, protected, and then "none", while it seems to me that it would be less confusing, and more consistent to use the keyword "package", or maybe even "default".
Then, source code would look like
public class MyClass{
    public int getValue() {}
    private void setValue() {}
    protected void someMethod() {}
    package int justForPackage() {}
}I know this concept has come up before, but the books I've read which mention this topic haven't offered any actaul justification/explanation for why there isn't some keyword.
Anyway, are there any insights as to why java is this way, and any reasons why java should or shouldn't be changed to include the package access modifier.

A good example is within a tightly grouped package (usually should be this way) you may have some cooperative classes that access methods.
// one .java file
public class SomeHelper {
   private void method() {
     new ClassForUsers().accessHiddenLogic();
// next .java file in same package
public ClassForUsers {
    /* default-access */ void accessHiddenLogic() {
}But, you may want to allow users to subclass your ClassForUsers, without giving them access to the hidden logic method directly:
// another .java file in a different package
public class UsersSubclass extends ClassForUsers {
    public void userMethod() {
        // can't do this
        accessHiddenLogic();
}This could be for either business logic or security reasons. So, package level access can be very useful. However, I've seen that in practice it is avoided because it isn't obvious what is going on.

Java class access modifiers

Why java class cannot have private and protected access modifiers?

class X {
private class y {}
}should compile just fine. A top-level private class makes no sense because you wouldn't be able to see it. As for protected, I don't know.

Inheritance and access control - "private protected"

I'm reopening an old topic, seems to have been last discussed here 2-3 years ago.
It concerns the concept of restricting access to class members to itself, and its subclasses. This is what "protected" does in C++ and "private protected" did in early versions of the Java language. This feature was removed from Java with a motivation along the lines of not being "simple", and "linear" (in line with the other access modes, each being a true subset of the next). Unfortunately, the article which explained Sun's position on this keyword combination seems to have been removed from the site, so I haven't been able to read its original text.
But regardless of simplicity of implementation or explaining Java's access modifiers to newbies, I believe it is a fundamental part of OO programming for such an access mode to exist. The arguments for having the standard "private" mode in fact also apply for having a C++-style "protected" mode. (Arguing that classes within a package are related and it therefore doesn't hurt to also give them access to Java's "protected" members, is equally arguing that "private" is unneccessary, which noone of course believes.)
The whole concept of inheritance and polymorphism and encapsulation builds on the access modes private, protected, and public (in the C++ senses). In Java the "package" concept was added - a nice feature! But I see no justification for it to negate the proper encapsulation of a class and its specializations.

What effect upon inheritance other than hiding members
from subclasses is there?
None. And I cant think of another declaration that prevents members from being inherited but private.
Of course the onus comes on the programmer with Java's
definition of "protected" - but
1) there is rarely a single programmer working within
a package
The point was the package is a unit which does not hide from itself. Just like all methods within a class can see each other, all classes within a package can, and all packages within a program can.
2) it muddies the encapsulation in the design - when
you see a "protected" method someone else, or yourself
some time ago - wrote, how do you know if the design
intention is to have it accessed solely by the class
and its subclasses, or if it is indeed intended to be
shared with the whole package? The only way to do
this today is to always explicitly specify this in the
comments, which may be lacking, inconsistent, and
abused (since it isn't enforced).Encapsulation would be implementation hiding. Not method hiding. The only thing you should probably allow out of your package is an interface and a factory anyway.
I understand where you are coming from, but I really have not had occasion to take issue with it. I can't think of a real codeing situation where this is required. OTOH, I can't think of a coding situation where I need to access a protected method from another class either.

Default class access modifier

What is the default access modifier for a class? I can't seem to find it in the tutorials...
Thanks
Jim

The default access is the same for top level classes that do not specify access explicitly as for other identifiers. Package.
This single source file will create two class files in the same package. Only other classes in the package can see these top level package access classes.
And, yes, this is a bad idea. In the case of some build tools, errors in a compile can cause the public class to compile, but the package class to fail. After that, the compiler will not be able to determine what source file to compile for the package level class. This is an error that confuses many developers. I do not recommend this practice. Put each top level class in its own source file.
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Access modifier for Constructors ???

As constructors are not the so called Members of a class
(Class's Member declarations include only 4 things : variables , methods, member classes and member interfaces)
Why do we have access modifiers for constructors also ??
I know that if a class A 's constructor is declared 'private' , then that class cannot be instantiated outside the class A. .That is, class A can be instantiated only inside class A and provide this newly created reference to the outside world through public getter method.
I dont understand how the other access modifiers (protected and default ) apply to a constructor.
Any help from ur side is greatly appreciated !!!!!

Why do we have access modifiers for constructors also
??To prevent anyone from accessing them if they shouldn't.
I know that if a class A 's constructor is declared
'private' , then that class cannot be instantiated
outside the class A. Or you use another c'tor. Or a static getInstance() method provided by A. You you simply shouldn't create an instance yourself anyway.
That is, class A can be
instantiated only inside class A and provide this
newly created reference to the outside world through
public getter method.Yepp.
I dont understand how the other access modifiers
(protected and default ) apply to a constructor. Same as at other places. No difference.

Use of public access modifier in main method

I want to know what is the significance of public access modifier with main (String args[]) method. Like generally we write
public static void main(String args[])
But if we write
private static void main(String args[])
OR
protected static void main(String args[])
then also its working properly.............
then what is the use of public keyword..........................
Regards
Ajay Pratap Singh

then what is the use of public keyword..........................Convention, I believe. And I think newer versions of the JVM require it.
P.S. Relax a bit on the punctuation overuse. Many folks around here find that a bit irritating, and you probably don't intend to send that kind of a message. Cheers!

Usage of default access modifier

Some programmers don't use the default access modifier (package level). Is there a specific reason? If so, what is it? Or is it a good to use default access modifier?
Thank you,
Srikanth

Some prefer to grant or limit access to an object by the interface they expose. In this case all methods are either public or private. Access is restricted based on the fact that only the appropriate code is given references of certain interface types and if code does not have the right interface, they can not access the method.
Its a different style, but I use it myself quite a bit. This way I never am concerned over if it should be public,private, protected or default. The choice is simpler. But sometimes it can make you create interfaces for really simple things which I am not uptight enough to do...

Overriding and Access Modifier

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