How marker interface works?

Marker interface have blank body containing nothing.
I want to know how implementing class start behaving in that manner or how marker interface technology work??

Marker interfaces are also called "tag" interfaces since they tag all the derived classes into a category based on their purpose. For example, all classes that implement the Cloneable interface can be cloned (i.e., the clone() method can be called on them). The Java compiler checks to make sure that if the clone() method is called on a class and the class implements the Cloneable interface. For example, consider the following call to the clone() method on an object o:
MyObject o = new MyObject();
MyObjectref = (MyObject)(o.clone());
If the class MyObject does not implement the interface Cloneable (and Cloneable is not implemented by any of the superclasses that MyObject inherits from), the compiler will mark this line as an error. This is because the clone() method may only be called by objects of type "Cloneable." Hence, even though Cloneable is an empty interface, it serves an important purpose.

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How are marker interfaces working ?

can we create user defined marker interface ?
Some thing like Serializable.
That is unless and untill a user implements Serializable interface he is not able to store the object to a persistance media.
The compiler shoud show errors if we are not implementing the ''user defined marker Interface'' which is used for some purpose
Something like we should be informing the compiler that if a user is not implementing a ''user defined marker interface'' he is not supposed to use a specific classes or methods in that class
Is it possible?????

Define a marker Interface like
public interface MyMarkerInterface {
}Now, you can use instanceof operator to determine whether a given object implements MyMarkerInterface or not. Like,
if (myObject instanceof MyMarkerInterface) {
System.out.println("Implements");
} else {
System.out.println("doesn't implement");
}

How local interfaces work in EJBs

How exactly local interfaces work in EJBs and how should I use them ?
Thank you.

They are simply non-RMI interface implementations that directly delgate to the EJB's implementation. They are called and in turn call the EJB just as you would call any normal class.
As such, there is no RMI or serialization overhead and the interfaces can include methods that update their arguments, something not possible in remote interfaces.
Generally speaking, you should define local interfaces for all entities as one seldom if ever would access entities remotely. You might even consider defining ONLY local interfaces for entities, but that is a tougher call.
You would define local interfaces for session EJB's that are invoked by other session EJB's within the same container. I would normally always define both local and remote interfaces unless there is some reason why I can eliminate one or the other.
Chuck

How does interface inheritance work ??

I have the following code. The printout is
Main
w
x
w
I don't understand how this is working. Clearly interface inheritance is working differently than normal class inheritance. Please explain.
thanks in advance.
kris.
The code follows
interface C
     char w = DD.echo ('w');
     char x = DD.echo ('x');
interface D extends C
     char y = DD.echo('y');
     char z = DD.echo('z');
     char a = DD.echo(w);
class DD implements D
     static char echo(char c)
          System.out.print(c + "\n");
          return c;
     public static void main (String args[])
          System.out.println("Main");
          DD dd = new DD();
          System.out.println(w + "\n");
}

The interface only needs loaded if one of its members
is accessed (although this is probably implemented
differently on different JVMs).No.
The interface is loaded.
It is not initialized. There is a difference. See section 12 of the JLS.
Assuming the above is true, it appears the following
is happening
1. C is loaded because w is accessed from DD�s main .
This loading causes �w� to be echoed and then �x� to
be echoed since loading the interface initializes the
members which in turn call the echo method (I am
assuming that this only happends when the members are
not �constants�).
2. The main method then echoes the w variable (which
is �w�).
Having said this, I would think this code would behave
differently on different JVMs so I am not sure how it
could even be a �good� theoretical question (unless
this is documented in the JLS).It is in the JLS.
Also, loading the the interface may not really be what
is happening; the initialization code may be in-lined
in the class (this could be tested by printing w twice
in main � really strange behaviour).No. It can't inline the initilization of one class in another class.

HT5293 how do i get my interfaces working

how do i get my interfaces working?

Which interfaces?
https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/ AppleHIGuidelines/Intro/Intro.html

JSF-Marker Interface

Hai Friends
I want to know what is use of marker interface in java(JSF) and also how it is working without having even single method declaration & definitions inside that interfece like Remote interface,serialization and so on.
Thanks
Selvakumar .k

Marker Interfaces work the same way as they do anywhere else. Please read about marker interfaces.

What is efax and how does it work?

Hi!
eFax® is a service provided by eFax®, not Hewlett-Packard, that allows you to send and receive faxes using the Internet rather than a phone line. eFax® is easy to use, but it is different than a typical phone-based fax machine. You don't require a phone line to use it, so you don't have to worry about busy signals and you can place your printer where you want it, not where the phone jacks are located! The fax number you are provided will not typically be a local number, and may even be in a different country. You will receive 20 incoming and 20 outgoing fax pages per month for free with this service. Your page counts will reset at midnight Pacific Time on the first of each month. You can also subscribe to eFax® Plus to obtain additional pages per month by visiting: http://www.eFax.com/products/internet-fax.
How does it work?
eFax® uses the printer Internet connection to send and receive faxes. When you send a fax, it is sent over the Internet to the eFax® server and then eFax® sends your fax to the recipient's fax machine over a standard phone line.
Your faxes are received in a similar manner, but the order is reversed. The sender sends the fax over a phone line to eFax® and then eFax® sends the fax to your printer using HP's ePrint service.
This question was solved.
View Solution.

Hi Im_cheesecake,
Great information, if you don't mind I just wanted to piggy back off of your post, to clear any potential confusion.
The 20 free incoming & 20 free outgoing faxes are with HP printer's that include the eFax service print app. As of now, we have three printer series' that include the pre-installed eFax print app: HP Photosmart 7510 Series, HP Envy 110 Series, and the HP Photosmart eStation C510a.
eFax also has a free plan which allows you to receive a limited number of faxes but does not allow you to send any faxes. If you exceed the number of received faxes allowed, eFax will prompt you to upgrade to a paying account. Here are the main details of the free plan:
One remote (i.e. non-local) eFax number
Area code/prefix is selected by eFax and cannot be changed (unless you upgrade to a paid account)
20 incoming fax pages per month (receive-only)
You are prompted to upgrade to a paying account if you exceed 20 incoming pages, or if you need send capability.
Say "Thanks" by clicking the blue Kudos Star in the post that helped you.
Please mark the post that solves your problem as "Accepted Solution"; therefore, it's easier for others to find.
I am an HP employee.

What is the significance of Marker interface? Why are we using, even though

What is the significance of Marker interface? Why are we using, even though it has no method?

Well, what's the significance of an interface? They can define a set of methods a class may implement but the class could equally well implement these methods without the interface so why having interfaces at all?
The answer is that the most important aspect of an interface is that it constitutes a type (you can declare variables of it). And it's a type regardless of how many methods it defines, including none. So the reason for having a marker interface is that you're interested solely in the type aspect of interfaces.

How to get work JavaFX WebViewBrowser sample in debian linux wheezy?

How to get work JavaFX WebViewBrowser sample in debian linux wheezy
You may also check latest version of this problem here...
The Starting point I have
Debian wheezy
java version "1.7.0_40"
Java(TM) SE Runtime Environment (build 1.7.0_40-b43)
Java HotSpot(TM) Client VM (build 24.0-b56, mixed mode)
GTK version: 2.24
NetBeans 7.3.1
Certified configuration acording to JavaFX Supported Configurations
is
Ubuntu 10.4 +
gtk2 2.18+
GTK is OK. do I require ubuntu?
first try: by downloading Java SE Downloads - javafx sample
Let's try it
zolta@zolta:~/dolgaim/IT/NetBeansProjects/javafx/javafx-samples-2.2.40$ java -jar SwingInterop.jar
# A fatal error has been detected by the Java Runtime Environment:
# SIGILL (0x4) at pc=0x9b6b4c22, pid=21172, tid=2658700144
# JRE version: Java(TM) SE Runtime Environment (7.0_40-b43) (build 1.7.0_40-b43)
# Java VM: Java HotSpot(TM) Client VM (24.0-b56 mixed mode linux-x86 )
# Problematic frame:
# C 0x9b6b4c22
# Core dump written. Default location: /home/zolta/dolgaim/IT/NetBeansProjects/javafx/javafx-samples-2.2.40/core or core.21172
# An error report file with more information is saved as:
# /tmp/hs_err_pid21172.log
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
Terminated
Let's see what core dump says
to be continued...

Gusar wrote:
We need *a lot* more info than that. Could be something very simple, like the interface being up before starting wifi-menu (netctl doesn't like the interface being up, it'll only start correctly if the interface is down).
Or it could be something more. In which case, you'll need to start wpa_supplicant manually with debugging enabled:
wpa_supplicant -i wlp18s0b1 -c <(wpa_passphrase MYSSID passphrase) -d
Once this says you're connected, open another terminal and start dhcpcd. Or, if wpa_supplicant doesn't manage to connect, post the *entire* output.
Edit: Ok, you posted more info as I was writing my post. Will look through that, maybe it contains something useful. If not, follow the instructions above.
Edit2: Nope, nothing about wireless in there, except that the driver loaded.
It worked!!
I was looking into the logs and found an authentication failure...my password is very long so I made some mistakes while typing it.
So this is the solution all the way:
SOLUTION:
- No need to install or load any external drivers (all I used was already in the base installation)
- DISABLE THE HIDDEN NETWORK OPTION IN THE ROUTER (thanks for the heads-up @Gusar)
- run "# wifi-menu"
or
"# wpa_supplicant -i [interface] -c <(wpa_passphrase MYSSID passphrase) -d"
- run "# dhcpcd [interface]"
- Good to go!!
I'm sorry for the trouble guys, and like I imagined, it was really easy and now I see my newbiness hahaha ;D
Thanks.

What is 'mobile account' and how does it work?

This is a hidden feature in Mac OS Leopard, that I believe require an Leopard Server on the network.
I have not found it in the regular user interface, but it can be revealed by following the below process:
1. Go to System Preferences > Accounts
2. Unlock
3. Search for mobile account, and press Enter
4. Wait for the Mobile account options to show up
What is this feature? How does it work?
I have found no references to it in the normal documentation.

Google is your friend:
"A mobile account is a Mac OS X Server user account that has been copied to a local computer and remains synchronized with the server account so that both locations contain a matching set of data."(Mac OS X Server User Management, p. 46).
And it has been around since 10.3, so it is not something new to Leopard.
see: http://www.afp548.com/articles/Panther/mcx2.html

How does serialization work.......!!

As Serializable interface is an MARKER interface and does not have any methods or field. Then how does a class implementing Serializable interface is automatically serialized(or the object is converted into bytestream).
Is it that, JVM does know what to do with a serialized object.
If this is the case, can I have a MARKER interface of my own, for a particular functionality.
with regards,
SHIRISH

As Serializable interface is an MARKER interface and
does not have any methods or field. Then how does a
class implementing Serializable interface is
automatically serialized(or the object is converted
into bytestream). They are not serialized automatically. There are methods available for that - ObjectInputStream.readObject() and ObjectOutputStream.writeObject().

How "DBMS_SPACE.UNUSED_SPACE" work

Dear Experts,
I want to know how "DBMS_SPACE.UNUSED_SPACE" work.
Then, I have two questions about this procedure.
1. Does the procedure gather information from CBO? or freelist of index ? or datablocks of index?
2. During the execution ,does the procedure lock the index for DML ?
Our system is SAP R/3 Enterprise 6.4.0 and Oracle 9.2.0.6.0.
Many Thanks,
Koji Kurosawa
Edited by: Kouji Kurosawa on Nov 26, 2009 11:41 AM

Hi
PLease see this link for more details on the package DBMS_SPACE.UNUSED_SPACE ;
http://download.oracle.com/docs/cd/B12037_01/appdev.101/b10802/d_space.htm#1000325
Also check this link for the various uses of the DBMS_SPACE package for space estimation in under various conditions
http://www.oracle.com/technology/pub/articles/10gdba/week15_10gdba.html
It also contains several examples.
Basically the Unused_Space tries to determine the amount of space below the High Water Mark which can be released to the System and which is un-necessary being held up due to frequent insertions and Deletions on OLTP Databases.
Thanks
Rishi

How does interfaces overcome the problem of single inheritance?

1) How does interfaces overcome the problem of single inheritance? Can anyone give an example of how it works?
2) In a Java book, I read: "Interfaces are implemented and used throughout the Java class library when behavior is expected to be implemented by a number of disparate classes."
Why does different classes require to implement a Java class library?
Can anyone please enlighten? Thanks.

>
2) In a Java book, I read: "Interfaces are implemented and used throughout the Java class library when behavior is expected to be implemented by a number of disparate classes."
Hi, let me try to explain this.
Say you have a left hand drive BMW and a right hand drive AUDI. typeOfDrive is a property for these two cars. If i am trying to make this property abstract, i will prefer to put this property in an Interface called Car. My classes BmwCar and AudiCar implement the Car Interface; by which they can use the property typeOfDrive.
So, the behaviour 'typeOfDrive'; when expected to be implemented by Disparate entities BmwCar and AudiCar, we try to abstract that property to a common Interface called Car.
interface Car {
String typeOfDrive;
String getTypeOfDrive();
class BmwCar implements Car {
String getTypeOfDrive() {
return typeOfDrive;
void setTypeOfDrive(String tod) {
this.typeOfDrive = tod;
class AudiCar implements Car {
String getTypeOfDrive() {
return typeOfDrive;
void setTypeOfDrive(String tod) {
this.typeOfDrive = tod;
}Now, when you create instance of your disparate classes, you will define the declared property 'typeOfDrive', as 'Left Hand Drive' for BmwCar and 'Right Hand Drive' for AudiCar.
So, "Interfaces are implemented and used throughout the Java class library when behavior is expected to be implemented by a number of disparate classes."
You can refer to many web wikis for better examples and explanations.
Regards,
~N~

How do interfaces have methods of Object class

Hi All,
Please consider the following code snippet.
public interface EmployeeService
    public void createEmployee(Employee emp);
    public Employee findEmployee(String empId);
public class EmployeeServiceImpl implements EmployeeService
    public void createEmployee(Employee emp) { ................. }
    public Employee findEmployee(String empId) { ................. }
}The above is a simple example where I have an employee object with two service methods to create and find an employee.
Now the consider the following
EmployeeService empService = new EmployeeServiceImpl();
Employee emp = empService.findEmployee("1").So the above code helps me in finding an employee.
Now, we know that you can only call those methods that are defined in the interface.
My question is, if I use the empService you would be able to access the methods of the Object class (equals, hashCode, wait etc.)
How does this happen? In the Jave API we know all class by default override the Object class, so how does it work with interfaces?
Thanks in advance for the reply

[JLS 6.4.4 The Members of an Interface Type|http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.4.4] says:
If an interface has no direct superinterfaces, then the interface implicitly declares a public abstract member method m with signature s, return type r, and throws clause t corresponding to each public instance method m with signature s, return type r, and throws clause t declared in Object, unless a method with the same signature, same return type, and a compatible throws clause is explicitly declared by the interface. It is a compile-time error if the interface explicitly declares such a method m in the case where m is declared to be final in Object.
So, in short, those methods exist in interfaces because the JLS says they do.

MARKER INTERFACE WHY?

hello i madhav new to this forum , i have doubt on marker interface . as it doesnot have any body why we r using that one instead of skipping.Is there any concept behind is there.More about my doubt is Take Example Cloneable Interface it Doesn't Have any Method In it,Clone() method is from Object class,then what is the necessity of implementing the interface .Why it should not be like that.
what is real technolgy behind MarkerInteface and Why we r going to be used in what situations it will needed.And Lastly is there any method related to Serailizable interface if not what it do .
marker interface can also called as Tag interface what is tag mean here just saying combing derived classes . i didn't get that one and how it will be .
if u could explain with example or real time project it would be better for me
thanks in advance

What is a "marker" interface?
Marker Interface pattern
c2.com - Marker Interface
experts.about.com - Marker Interfaces
The Purpose of the Marker Interface
Maximize your Design ROI with Marker Interfaces and JavaDoc

How marker interface works?

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