Difference b/w class & instace variable

can any one plz tell me the difference b/w class variable & instance variable.

what about googling for "java class instance" ?

Similar Messages

Difference between Abstract Classes Vs Interface

Hi,
Can u pls mention all the differences between Abstract Classes and Interface.? I've mentioned the differences I've known here.
Known Differences:
(*) An interface cannot implement any methods, whereas an abstract class can.
(*) A class can implement many interfaces but can have only one superclass
Can U pls mention at what situation(practical situation) we've to go for abstract class or Interface?
Tell me the situation when we have to go for abstract class?
Tell me the situation when we have to go for interface?
Please Reply me
Thanks & Regards
Venkatesh

There are more differences, and one really important is that abstract classes can also define class variables, while interfaces cannot. I think the question of when to use interfaces or abstract classes is not always easy to answer, but yourself have pointed some tips you should be aware of :
If you need that some funcionality of the class is derived by more than one "parent" then you should use interfaces, since you cannot extend more than one class.
If your "superclass" needs to define some class variables then the choice must be made to have a superclass and then extend it. Also this is applicable if there is a method that can be programmed at a higher level (in interfaces you cannot program methods).
But the answer to the question is still not easy. And remember, you can always mix both tipes, you can extend one class and implement some interfaces.
Examples or that are very common in the Java API for AWT or Swing components, for example javax.swing.JLabel extends javax.swing.JComponent (that is beacuse a JLabel IS a JComponent and it uses some variables and methods programmed at the JComponent "level") and it also implements some interfaces: Accessible, ImageObserver, MenuContainer, Serializable & SwingConstants.
I hope this helps.
Zerjillo

Difference between Java class and JavaBean?

What is the difference between a Java class and a JavaBean?
A class has variables which hold state.
A class has methods which can do things (like change state).
And if I understand a JavaBean it is rather like a BIG class...
i.e.
A JavaBean has variables which hold state.
A JavaBean has methods which can do things (like change state).
So, what's the difference between the two?
And in case it helps...What is the crossover point between the two? Is there a minimalist type JavaBean which is the same as a class? What is the difference between Java beans and Enterprise Java Beans?
Thanks.

Introspection, as I understand it is a bunch of
methods which allows me to ask what a class can do
etc. right? So, if I implement a bunch of
introspection methods for my class then my class
becomes a JavaBean?Introspection allows a builder tool to discover a Bean's properties, methods, and events, either by:
Following design patterns when naming Bean features which the Introspector class examines for these design patterns to discover Bean features.
By explicitly providing the information with a related Bean Information class (which implements the BeanInfo interface).
I understand now they are completely different.
Thanks. Very clear.
I do not understand how they are completely different.
In fact I don't have a clue what the differences are
other than to quote what you have written. In your
own words, what is the difference? This is the "New
to Java Technology" forum ;-) and I'm new to these
things.In that case ejbs are way too advanced for you, so don't worry about it.

Difference between Temp table and Variable table and which one is better performance wise?

Hello,
Anyone could you explain What is difference between Temp Table (#, ##) and Variable table (DECLARE @V TABLE (EMP_ID INT)) ?
Which one is recommended to use for better performance?
also Is it possible to create CLUSTER and NONCLUSTER Index on Variable table?
In my case: 1-2 days transactional data are more than 3-4 Millions. I tried using both # and table variable and found table variable is faster.
Is that Table variable using Memory or Disk space?
Thanks Shiven:) If Answer is Helpful, Please Vote

Check following link to see differences b/w TempTable & TableVariable: http://sqlwithmanoj.com/2010/05/15/temporary-tables-vs-table-variables/
TempTables & TableVariables both use memory & tempDB in similar manner, check this blog post: http://sqlwithmanoj.com/2010/07/20/table-variables-are-not-stored-in-memory-but-in-tempdb/
Performance wise if you are dealing with millions of records then TempTable is ideal, as you can create explicit indexes on top of them. But if there are less records then TableVariables are good suited.
On Tables Variable explicit index are not allowed, if you define a PK column, then a Clustered Index will be created automatically.
But it also depends upon specific scenarios you are dealing with , can you share it?
~manoj | email: http://scr.im/m22g
http://sqlwithmanoj.wordpress.com
MCCA 2011 | My FB Page

What is the difference between document class and normal class

Hi,
Please let me know what is the difference between document class and normal class.
And I have no idea which class should call as document class or call as an object.
Thanks
-Actionscript Developer

the document class is invoked immediately when your swf opens. the document class must subclass the sprite or movieclip class.
all other classes are invoked explicitly with code and need not subclass any other class.

Binding a JavaFX variable to a Java class instance variable

Hi,
I am pretty new to JavaFX but have been developing in Java for many years. I am trying to develop a JavaFX webservice client. What I am doing is creating a basic scene that displays the data values that I am polling with a Java class that extends Thread. The Java class is reading temperature and voltage from a remote server and storing the response in an instance variable. I would like to bind a JavaFx variable to the Java class instance variable so that I can display the values whenever they change.
var conn: WebserviceConnection; // Java class that extends Thread
var response: WebserviceResponse;
try {
conn = new WebserviceConnection("some_url");
conn.start();
Thread.sleep(10000);
} catch (e:Exception) {
e.printStackTrace();
def bindTemp = bind conn.getResponse().getTemperature();
def bindVolt = bind conn.getResponse().getVoltage();
The WebserviceConnection class is opening a socket connection and reading some data in a separate thread. A regular socket connection is used because the server is not using HTTP.
When I run the application, the bindTemp and bindVolt are not updated whenever new data values are received.
Am I missing something with how bind works? Can I do what I want to do with 'bind'. I basically want to run a separate thread to retrieve data and want my UI to be updated when the data changes.
Is there a better way to do this than the way I am trying to do it?
Thanks for any help in advance.
-Richard

Hi,
If you don't want to constantly poll for value change, you can use the observer design pattern, but you need to modify the classes that serve the values to javafx.
Heres a simple example:
The Thread which updates a value in every second:
// TimeServer.java
public class TimeServer extends Thread {
    private boolean interrupted = false;
    public ValueObject valueObject = new ValueObject();
    @Override
    public void run() {
        while (!interrupted) {
            try {
                valueObject.setValue(Long.toString(System.currentTimeMillis()));
                sleep(1000);
            } catch (InterruptedException ex) {
                interrupted = true;
}The ValueObject class which contains the values we want to bind in javafx:
// ValueObject.java
import java.util.Observable;
public class ValueObject extends Observable {
    private String value;
    public String getValue() {
        return this.value;
    public void setValue(String value) {
        this.value = value;
        fireNotify();
    private void fireNotify() {
        setChanged();
        notifyObservers();
}We also need an adapter class in JFX so we can use bind:
// ValueObjectAdapter.fx
import java.util.Observer;
import java.util.Observable;
public class ValueObjectAdapter extends Observer {
    public-read var value : String;
    public var valueObject : ValueObject
        on replace { valueObject.addObserver(this)}
    override function update(observable: Observable, arg: Object) {
         // We need to run every code in the JFX EDT
         // do not change if the update method can be called outside the Event Dispatch Thread!
         FX.deferAction(
             function(): Void {
                value = valueObject.getValue();
}And finally the main JFX code which displays the canging value:
// Main.fx
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.text.Text;
import javafx.scene.text.Font;
import threadbindfx.TimeServer;
var timeServer : TimeServer;
var valueObjectAdapter : ValueObjectAdapter = new ValueObjectAdapter();
timeServer = new TimeServer();
valueObjectAdapter.valueObject = timeServer.valueObject;
timeServer.start();
Stage {
    title: "Time Application"
    width: 250
    height: 80
    scene: Scene {
        content: Text {
            font : Font {
                size : 24
            x : 10, y : 30
            content: bind valueObjectAdapter.value;
}This approach uses less cpu time than constant polling, and changes aren't dependent on the polling interval.
However this cannot be applied to code which you cannot change obviously.
I hope this helps.

Class/member variables usage in servlets and/or helper classes

I just started on a new dev team and I saw in some of their code where the HttpSession is stored as a class/member variable of a servlet helper class, and I was not sure if this was ok to do or not? Will there be problems when multiple users are accessing the same code?
To give some more detail, we are using WebLogic and using their Controller (.jpf) files as our servlet/action. Several helper files were created for the Controller file. In the Controller, the helper file (MyHelper.java) is instantiated, and then has a method invoked on it. One of the parameters to the method of the helper class is the HttpServletRequest object. In the method of the helper file, the very first line gets the session from the request object and assigns it to a class variable. Is this ok? If so, would it be better to pass in the instance of the HttpServletRequest object as a parameter to the constructor, which would set the class variable, or does it even matter? The class variable holding the session is used in several other methods, which are all invoked from the method that was invoked from the Controller.
In the Controller file:
MyHelper help = new MyHelper();
help.doIt(request);MyHelper.java
public class MyHelper {
    private HttpSession session;
    public void doIt(HttpServletRequest request) {
        session = request.getSession();
        String temp = test();
    private String test() {
        String s = session.getAttribute("test");
        return s;
}In the past when I have coded servlets, I just passed the request and/or session around to the other methods or classes that may have needed it. However, maybe I did not need to do that. I want to know if what is being done above will have any issues with the data getting "crossed" between users or anything of that sort.
If anyone has any thoughts/comments/ideas about this I would greatly appreciate it.

No thoughts from anyone?

What are the basic difference in the putting a variable in Query

what are the basic difference in the putting a variable in
1. Characteristic Restrictions Vs 2. Default Values

Example - Cost Center Analysis Report - If I have Controlling Area in
Char Restricitons Only - I have restricted it to say ABC Controlling Area or a Variable- Report will be hardcoded to ABC Controlling Area or the Input Value entered during Runtime - After Execution, The Same cannot be changed in the report.
Assuming I will not have Controlling Area in the report means not in Rows n Columns.
You might have seen no change - > Did you place material in Rows or Columns ?

Creating class wide variable that gets re-initialized every time

I declared a class-wide variable in my jsp document using the <%! %> tags:
<%! boolean HasMoreRows = true %>
I set this variable to false in one of the private jsp methods (also declared within <%! %> tags) when the program is supposed to terminate (there are no more rows left in my database result set).
When I run the jsp document the first time after modifying it, it works fine. But if I hit the browser "back" button and then hit the "submit" button on the jsp page again to recreate the database result set, the HasMoreRows variable has the same value it had after the report ran the first time (that is, it is set to false).
I think this has something to do with the way a servlet is created and re-used by the servlet container. I have to set the variable in a method so I cannot use a local variable (i.e. a variable declared inside <% %> tags). Does anyone know how to declare a variable that can be used anywhere inside the jsp document (including all methods) but gets reset to its initialization value every time the jsp document is run? Thanks.

I think I figured out the solution. It is to declare the variable in the <%! %> tags but initialize it in the <% %> tags.
<%! boolean HasMoreRows; %>
<% HasMoreRows = true; %>

Whats the difference betweeen passing the table variable and table valued parameter?

Hi Everbody
Can someone one tell me what's the difference between passing a table variable and table valued parameter to a stored procedure or function? Can both be used to pass a table to a stored procedure/function?
Regards
Regards

They are essentially the same. What we call a table variable is a local
variable. A table-valued parameter is an incoming parameter to the
procedure. The only difference is that the parameter is readonly.
When you call a stored procedure, you can pass a table variable as the
actual parameter. Or a table-valued parameter that you pass on.
CREATE PROCEDURE nisse_sp @tvp sometype READONLY AS
DECLARE @local someothertabletype
EXEC pelle_sp @tvp, @local
Erland Sommarskog, SQL Server MVP, [email protected]

What is the difference between Abstract class and Interface ?

Hi,
Could u plz tell me the difference between Abstract class and Interface?
Thanks in advance.
Gopi

Lots.
An abstract class can contain some method implementations, or indeed all the method implementations. It may contain methods with all the various access modifiers. It cannot be instantiated. A class may inherit from only a single abstract class.
An interface contains only public method stubs and constants. A class may implement multiple interfaces. An interface cannot (obviously) be instantiated.
Abstract classes are particularly useful when you need to provide a semi-complete implementation for reuse. Interfaces are used more like types.
Look at java.util.* for some good examples of the use of both.

Difference between Abstarct Class and Interface

HI,
Here is a simple one for the gurus but quite important for me.
What is the difference b/w an Interface and an abstract class?
Why do we need each one of them?
I would appreciate if you people can give examples of each so that I amy understand fully
Thanks in advance...

A normal class (not abstract) has a special behaviour, like java.awt.Frame. A Frame is a frame no matter how you subclass it. If you create a subclass it will still be able to be displayed by calling it's show method. So by using a normal class you can create a type of class.
An abstract class does the same, but it leaves some of the code unwritten. For instance java.lang.Number. This class is abstract becuase it has no knowledge of how to store the number in memory. But it knows that it is a number, and any subclass will still be a number. You could create a subclass of Number that can hold the time in milliseconds and checks your system clock to see what the time is, it could also have methods that return the time in another country, but it would still be just a Number.
An interface is a way to describe what an object can do, not what it is. So with java.lang.Comparable as an example you can make any class comparable. This means that no matter what type of object you have, it can be compared with other objects. So you can have a subclass of Frame that can be compared with other windows. Or a subclass of Number that can be compared with other Numbers. You can even compare those two different types if you like. So you could compare a window with a number.
That is the difference between abstract classes and interfaces.
I hope you could follow my arguments, it isn't an easy subject,
Daniel

What's the difference between batch class type 022 and 023?

Hi Guys,
I find that some of my SAP client only have class 022 and some have 023, but no client has them all. I don't know why it happed.
So what's the difference between batch class type 022 and 023? Which setting decide which class to be used ?
Thanks.

Hi nitin,
Read http://www.sapfans.com/forums/viewtopic.php?t=212819&highlight=022 you will know the difference between 022 and 023 .
Use tcode OMCT you can switch batch level .

The difference between batch class type 022 and 023

what's difference between batch class type 022 and 023? 023 is described as standard batch class type, but there is only 022 type exists in my system. can i use 022?

Hi,
both classes mean the same, but which class is used is decieded by batch level. In case of material level or client level the system use automatically only class 023. If you define batch level to plant the system use automatically class 022.
Regards,
Abhee.

OAB - difference between standard rate and variable rate

What is the difference between standard rates and variable rates

These Variable rates will take into effect only when you check the "uses variable rate" check box in standard rate right?
Yes, variable rates are evaluated only if this flag is selected.
You mentioned Standard Rate is the rate you attach to a benefit. Where do we attach?
You donot attach the rate to a benefit in a separate form. You select the compensation object you want to attach the rate to within the standard rates form.

Difference b/w class & instace variable

Similar Messages

Maybe you are looking for