I really need abstract static methods in abstract class

Hello all.. I have a problem,
I seem to really need abstract static methods.. but they are not supported.. but I think the JVM should implement them.. i just need them!
Or can someone else explain me how to do this without abstract static methods:
abstract class A {
abstract static Y getY();
static X getX() {
    // this methods uses getY, for example:
    y=getY();
   return new X(y); // or whatever
class B extends A {
static Y getY() { return YofB; }
class C extends A {
static Y getY() { return YofC; }
// code that actually uses the classes above:
// these are static calls
B.getX();
A.getX();I know this wont compile. How should i do it to implement the same?

Damn i posted this in the wrong thread.. anyways.
Yes offcourse i understand abstract and static
But i have a problem where the only solution is to use them both.
I think it is theoretically possible ot implement a JVM with support for abstract static methods.
In fact it is a design decision to not support abstract static methods.. thats why i am asking this question.. how could you implemented this otherwise?
There is an ugly soluition i think: using Aspect Oriented Programming with for example AspectJ.. but that solution is really ugly. So anyone has an OO solution?

Similar Messages

Why do we need private static method or member class

Dear java gurus,
I have a question about the use of private and static key words together in a method or inner class.
If we want to hide the method, private is enough. a private static method is sure not intended to be called outside the class. So the only usage I could see is that this private static method is to be called by another static method. For inner class, I see the definition of Entry inner class in java.util.Hashtable, it is static private. I don't know why not just define it as private. Could the static key word do anything better.
Could anybody help me to clear this.
Thanks,

What don't you get? Private does one thing, andstatic does >something completely different.
If you want to listen to music, installing an airconditioner doesn't help>
Hi, if the private keyword is the airconditioner, do
you think you could get music from the static keyword
(it acts as the CD player) in the following codes:You're making no sense and you're trying to stretch the analogy too far.
Private does one thing. If you want that thing, use private.
Static does something completely different and unrelated. If you want that thing, use static.
If you want both things, use private static.
What do you not understand? How can you claim that you understand that they are different, and then ask, "Why do we need static if we have private"? That question makes no sense if you actually do understand that they're different.

Static methods in startup class

I have declared few static methods in startup class. What will happen
          once startup class is executed in cluster environment, will the access
          to those static methods be clustered and replicated across the
          clusters. How exactly the startup class behaves in clustered
          environment.
          I will appreciate an urgent response.
          Thanks,
          SidShar .


SidShar,
          > I have declared few static methods in startup class. What will
          > happen once startup class is executed in cluster environment,
          > will the access to those static methods be clustered and
          > replicated across the clusters.
          No.
          > How exactly the startup class behaves in clustered environment.
          It is run on each server that it is configured to run on. The method calls
          to the startup class will all be local unless you do some special work to
          force it to be otherwise.
          If you want to have something done once and only once in the cluster, or
          coordinate stuff like that, then either use a shared resource (such as the
          database) to coordinate it all, or use Coherence, which lets you share and
          coordinate access to data among all the servers in the app tier.
          Peace,
          Cameron Purdy
          Tangosol, Inc.
          http://www.tangosol.com/coherence.jsp
          Tangosol Coherence: Clustered Replicated Cache for Weblogic
          "sidshar" <[email protected]> wrote in message
          news:[email protected]..
          >

I am not able access static methods from startup class

I have a simple java class which queries the Database and holds some data. I am trying to access a static method of this class from the StartupClass and I am not able to do so. But I am able to access a static variable of the same class.
Can someone help me here.

Well, welcome to the world of "hacked" phones. If your purchase was from the US, you obviously purchased an iPhone that is locked to a US carrier. The iPhone must have been jailbroken and unlocked via software to accommodate your foreign SIM card. Now that you have updated the phone, it is locked back to the US carrier. Only the carrier can authorize Apple to unlock the iPhone and none of the US carriers will unlock the iPhones. Best suggestion is to sell the phone and obtain a factory unlocked version directly from the Apple store.
To answer your other question, there is not a supported method to downgrade iOS.

How to find the arguments of a static method from the class file

Hi,all !
How to find the arguments of a static method from the class file? for example, when we meet a bytecode "invokestatic", how can I know the arguments of this static method?

Hi,all !
How to find the arguments of a static method from the
class file? for example, when we meet a bytecode
"invokestatic", how can I know the arguments of this
static method?You mean
1. The values?
2. Argument names?
3. Argument signatures.
I would suppose for the last that the easiest way would be to parse the signature string.
The first is not possible - not from the class file.
The second is only in the debug information stored in the optional part of the class file. And figuring out the format for that is going to be a problem.

What is the purpose of Static methods inside a class?

Hi,
What is the purpose of Static methods inside a class?
I want the answers apart from "A static method does not require instance of class(to access) and it can directly be accessed by the class name itself"
My question is what is the exact purpose of a static method ?
Unlike attributes, a separate copy of instance attributes will be created for each instance of a class where as only one copy of static attributes will be created for all instances.
Will a separate copy of instance method be created for each instance of a class and only one copy of static methods be create?
Points will be rewarded for all helpful answers.

Hi Sharma,
Static methods is used to access statics attributes of a class. We use static attributes when we want to share the same attribute with all instances of a class, in this case if you chage this attribute through the instance A this change will change will be reflected in instance B, C........etc.
I think that your question is correct -> a separate copy of instance method will be created for each instance of a class and only one copy of static methods be create ?
"A static method does not require instance of class(to access) and it can directly be accessed by the class name itself"
Static Method: call method class=>method.
Instance Method: call method instance->method.
Take a look at this wiki pages.
[https://wiki.sdn.sap.com/wiki/x/o5k]
[https://wiki.sdn.sap.com/wiki/x/ZtM]
Best regards.
Marcelo Ramos

How to call a static method in a class if I have just the object?

Hello. I have an abstract class A where I have a static method blah(). I have 2 classes that extend class A called B and C. In both classes I override method blah(). I have an array with objects of type B and C.
For every instance object of the array, I'm trying to call the static method in the corresponding class. For objects of type B I want to call blah() method in B class and for objects of type C I want to call blah() method in C class. I know it's possible to call a static method with the name of the object, too, but for some reason (?) it calls blah() method in class A if I try this.
So my question is: how do I code this? I guess I need to cast to the class name and then call the method with the class name, but I couldn't do it. I tried to use getClass() method to get the class name and it works, but I didn't know what to do from here...
So any help would be appreciated. Thank you.

As somebody already said, to get the behavior you
want, make the methods non-static.You all asked me why I need that method to be
static... I'm not surprised to hear this question
because I asked all my friends before posting here,
and all of them asked me this... It's because some
complicated reasons, I doubt it.
the application I'm writing is
quite big...Irrelevant.
Umm... So what you're saying is there is no way to do
this with that method being static? The behavior you describe cannot be obtained with only static methods in Java. You'd have to explicitly determine the class and then explicitly call the correct class' method.

Apply static method requirements on class (Static interface methods)?

I have a set of classes where is class is identified with a unique ID number. So each class has a public static int getId() method. Each class also has either a constructor that takes a byte array or a static factory method that takes a byte array.
I would like to maintain a hashmap of these classes keyed to the ID's however I am not sure how to have some interface of abstract parent class that requires each of these classes to implement these static methods.
What I was hoping to do was something like this>>>
     public interface MyClasses{
          static MyClasses createInstance(byte[] data);
     HashMap<Integer, MyClasses> map;
     public void init() {
          map = new HashMap<Integer, MyClasses>();
          map.put(Class1.getId(), Class1.class);
          map.put(Class2.getId(), Class2.class);
     public void createInstance (int id, byte[] data) {
          map.get(id).createInstance(data);
     }Is there some way I could do this?

What about something like this?
public interface Initializable
     public void initialize(byte[] data);
public class Factory
     private final Map<Integer, Initializable> map = new HashMap<Integer, Initializable>();
        public void registerClass(int id, Class klass)
                if (! Initializable.class.isAssignableFrom(klass))
                         // you may also want to ensure the class declares a parameterless constructor
                         throw new IllegalArgumentException("duff class");
                if (this.map.keySet().contains(id))
                         throw new IllegalArgumentException("duff id");
          this.map.put(id, klass);
     public Initializable createInstance(int id, byte[] data)
                // need some exception handling of course
          Initializable i = map.get(id).newInstance();
                i.initialize(data);
                return i;
}

Compilation error while calling static method from another class

Hi,
I am new to Java Programming. I have written two class files Dummy1 and Dummy2.java in the same package Test.
In Dummy1.java I have declared a static final variable and a static method as you can see it below.
package Test;
import java.io.*;
public class Dummy1
public static final int var1= 10;
public static int varDisp(int var2)
return(var1+var2);
This is program is compiling fine.
I have called the static method varDisp from the class Dummy2 and it is as follows
package Test;
import java.io.*;
public class Dummy2
public int var3=15;
public int test=0;
test+=Dummy1.varDisp(var3);
and when i compile Dummy2.java, there is a compilation error <identifier > expected.
Please help me in this program.

public class Dummy2
public int var3=15;
public int test=0;
test+=Dummy1.varDisp(var3);
}test+=Dummy1.varDisplay(var3);
must be in a method, it cannot just be out somewhere in the class!

Calling a non-static method from another Class

Hello forum experts:
Please excuse me for my poor Java vocabulary. I am a newbie and requesting for help. So please bear with me! I am listing below the program flow to enable the experts understand the problem and guide me towards a solution.
1. ClassA instantiates ClassB to create an object instance, say ObjB1 that
    populates a JTable.
2. User selects a row in the table and then clicks a button on the icon toolbar
    which is part of UIMenu class.
3. This user action is to invoke a method UpdateDatabase() of object ObjB1. Now I want to call this method from UIMenu class.
(a). I could create a new instance ObjB2 of ClassB and call UpdateDatabase(),
                                  == OR ==
(b). I could declare UpdateDatabase() as static and call this method without
     creating a new instance of ClassB.With option (a), I will be looking at two different object instances.The UpdateDatabase() method manipulates
object specific data.
With option (b), if I declare the method as static, the variables used in the method would also have to be static.
The variables, in which case, would not be object specific.
Is there a way or technique in Java that will allow me to reference the UpdateDatabase() method of the existing
object ObjB1 without requiring me to use static variables? In other words, call non-static methods in a static
way?
Any ideas or thoughts will be of tremendous help. Thanks in advance.

Hello Forum:
Danny_From_Tower, Encephalatic: Thank you both for your responses.
Here is what I have done so far. I have a button called "btnAccept" created in the class MyMenu.
and declared as public.
public class MyMenu {
    public JButton btnAccept;
     //Constructor
     public MyMenu()     {
          btnAccept = new JButton("Accept");
}     I instantiate an object for MyMenu class in the main application class MyApp.
public class MyApp {
     private     MyMenu menu;
     //Constructor
     public MyApp(){
          menu = new MyMenu();
     public void openOrder(){
           MyGUI MyIntFrame = new MyGUI(menu.btnAccept);
}I pass this button all the way down to the class detail02. Now I want to set up a listener for this
button in the class detail02. I am not able to do this.
public class MyGUI {
     private JButton acceptButton;
     private detail02 dtl1 = new detail02(acceptButton);
     //Constructor
     public AppGUI(JButton iButton){
     acceptButton = iButton;
public class detail02{
    private JButton acceptButton;
    //Constructor
    public detail02(JButton iButton){
      acceptButton = iButton;
      acceptButton.addActionListener(new acceptListener());
   //method
    private void acceptListener_actionPerformed(ActionEvent e){
       System.out.println("Menu item [" + e.getActionCommand( ) + "] was pressed.");
    class acceptListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
               acceptListener_actionPerformed(e);
} I am not able to get the button Listener to work. I get NullPointerException at this line
          acceptButton.addActionListener(new acceptListener());in the class detail02.
Is this the right way? Or is there a better way of accomplishing my objective?
Please help. Your inputs are precious! Thank you very much for your time!

Calling a static method from another class

public class Command
    public static void sortCommands(String command, String order, List object)
         if(command.equalsIgnoreCase("merge") && order == "a")
              object.setAscending(true);
              Mergesort.mergesort(object.list);                  // line 85
}and
public class Mergesort
     public static void mergesort (int[] a)
          mergesort(a, 0, a.length-1);
     private static void mergesort (int[] a, int l, int r)
     private static void merge (int[] a, int l, int m, int r)
}Error:
Command.java:85: cannot find symbol
symbol : variable Mergesort
location: class Command
Mergesort.mergesort(object.list)
What am I doing wrong here? Within the Command class I am calling mergesort(), a static method, from a static method. I use the dot operator + object so that the compiler would recognize the 'list' array. I tried using the
Mergesort.mergesort(object.list);notation in hopes that it would work like this:
Class.staticMethod(parameters);but either I am mistaken, misunderstood the documentation or both. Mergesort is not a variable. Any help would be appreciated, I have been hitting a brick wall for hours with Java documentation. Thanks all.

[Javapedia: Classpath|http://wiki.java.net/bin/view/Javapedia/ClassPath]
[How Classes are Found|http://java.sun.com/j2se/1.5.0/docs/tooldocs/findingclasses.html]
[Setting the class path (Windows)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/classpath.html]
[Setting the class path (Solaris/Linux)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/classpath.html]
[Understanding the Java ClassLoader|http://www-106.ibm.com/developerworks/edu/j-dw-javaclass-i.html]
java -cp .;<any other directories or jars> YourClassNameYou get a NoClassDefFoundError message because the JVM (Java Virtual Machine) can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.
javac -classpath .;<any additional jar files or directories> YourClassName.javaYou get a "cannot resolve symbol" message because the compiler can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.

Static methods in javafx class.

How do I create static methods in javafx similar to static methods in java?

Hi swamyv,
I haven't tried declaring any static functions but I know that you can declare static variables by placing them in the script file, but not inside a class definition.
Something like this:
package com.mycompany.somepackage;
public static def ID:String = "someString";
public class SomeClass {
}In this case you refer to the static variable by the name of the file, not the name of the class (even though they might be the same).
e.g. If the above code was in a file called SomeFile.fx, you would refer to the variable as SomeFile.ID.
Maybe you could try defining a function in the same way.
Cheers,
Kevin

How to call a static method of a class from another class?

Hello,
I have two classes in a package. The first one
package my package;
public class class1
protected static ImageIcon createIcon(String path)
The second one
package my package;
public class class2
private ImageIcon image1;
image1 = class1.createIcon("/mypath");
This does not work since class2 cannot load the appropriate image. Where do I have to define the ImageIcon variables in class one or two and do they have to be static variables?
Thanks in advance
Christos

If the two classes are in the same package, that will work, in fact. A trivial example:
package foo;
public class Foo1 {
     protected static String getString() {
          return "World";
// Note: Member of the same package
package foo;
public class Foo2 {
     public static void main(String[] argv) {
          System.out.println("Hello "+ foo.Foo1.getString());
}However, if they are in different packages that won't work - the protected keyword guarantees that only classes derived from the class with the protected method can access it: Therefore this will not work:
package foo;
public class Foo1 {
     protected static String getString() {
          return "World";
package foo.bar;
public class Foo2{
     public static void main(String[] argv) {
          System.out.println("Hello "+ foo.Foo1.getString());
}But this will:
package foo;
public class Foo1 {
     protected static String getString() {
          return "World";
package foo.bar;
public class Foo2 extends foo.Foo1 {
     public static void main(String[] argv) {
          System.out.println("Hello "+ foo.Foo1.getString());
}I think you should read up a bit more about packages and inheritance, because you're going to have a lot of trouble without a good understanding of both. Try simple examples first, like the above, and if you hit problems try to produce a simple test case to help you understand the problem rather than trying to debug your whole application.
Dave.

Static Methods in Util class

Dear Gurus,
I am new to Java and working on a Java Web Application which is already running.
1)
I found that the util class methods are static also not Synchoronised.
I feel this is wrong because if any 2 user accesses the methods concurrently
then those 2 users will not get expected results.
2)
Basically servlets are not thread safe. Then how actually it serves different users who are accessing
concurrently without any issues.
Can any one please clarify me the doubts?
Thanks in advance
Goudham

You can declare servlets to be multithreaded. Servlet
containers are supposed to be able to instanciate a
different instance of a servlet for every simultanious
request if you tell it to in the servler descriptor.
Tomcat does this, and I'm sure that WebLogic, BEA,
and the Sun on do as well. That way you don't have
to worry about multi-requests hitting one instance of
a servlet object. This does add more overhead, but
sometimes that's ok.To be more precise, you can declare servlets to be non-thread-safe (i.e. SingleThreadModel). This has the affect of preventing concurrent requests from being dispatched to the Servlet instance. Most (in my experience, all) Servlet containers provide the means by which you can set the maximum size of the instance pool for a SingleThreadModel servlet.
Your best bet is to make your Servlet classes stateless and therefore inherently thread safe. To do this, simply don't define any non-final static or non-static fields and never change the state of those fields). This gives you the greatest scalability. If you must, then have your Servlet implement SingleThreadModel and define an appropriately sized instance pool.
Of course this won't do anything directly to deal with helper classes and their thread safety issues.
Chuck

How to call a static method of a class (continued)

In reference to the above topic posted one week ago I give you the relative code. The problem is resolved and it was the following one (amazing for me since I looked for any possible error in the code like the one posted in my article but I could never imagine this trivial thing.........):
the package name which is the directory with the appropriate class files should not extend the lenght of 8 characters!!! Initially I had a package named Applications (too long for DOS...) and when I renamed it to Test everything worked. Any suggestion on how to overcome this DOS filesystem problem?
Christos
Here is my simplified code
     package test;
     import java.io.*;
     import java.net.URL;
     import javax.swing.*;
     import java.beans.*;
     import java.awt.*;
     import java.awt.event.*;
     public class myapplet extends JApplet
     private MyClass myframe;
     private JDesktopPane desktop;
     private Dimension d;
public void init() {
myframe= new MyClass();
desktop = new JDesktopPane();
d=desktop.getSize();
try {
javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
createGUI();
} catch (Exception e) {
System.err.println("createGUI didn't successfully complete");
     private void createGUI() {
     myframe.pack();
     myframe.setBounds(0,0,d.width,d.height);
     desktop.add(myframe);
     this.getContentPane().add(desktop);
     try {
     myframe.setMaximum(true);
     } catch (PropertyVetoException e) {
     e.printStackTrace();
     myframe.setVisible(true);
protected static ImageIcon createAppletImageIcon(String path,
String description)
int MAX_IMAGE_SIZE = 75000; //Change this to the size of
//your biggest image, in bytes.
int count = 0;
BufferedInputStream imgStream = new BufferedInputStream(
myapplet.class.getResourceAsStream(path));
if (imgStream != null)
byte buf[] = new byte[MAX_IMAGE_SIZE];
try {
count = imgStream.read(buf);
} catch (IOException ieo) {
System.err.println("Couldn't read stream from file: " + path);
try {
imgStream.close();
} catch (IOException ieo) {
System.err.println("Can't close file " + path);
if (count <= 0) {
System.err.println("Empty file: " + path);
return null;
return new ImageIcon(Toolkit.getDefaultToolkit().createImage(buf),
description);
} else {
System.err.println("Couldn't find file: " + path);
return null;
followed by the class MyClass
package test;
     import javax.swing.*;
     import java.awt.*;
     import java.awt.event.*;
     public class MyClass extends JInternalFrame
     private JLabel jl;
     private String myicon1="images/myimage.gif";
     private ImageIcon image1;
     public MyClass()
     super ( "This is my application",false,true,true,false);
     setDefaultCloseOperation(DISPOSE_ON_CLOSE);
image1= myapplet.createAppletImageIcon(myicon1,"");
jl = new JLabel("This is my image",
          image1,JLabel.CENTER);
jl.setFont (new Font("Times-Roman",Font.BOLD, 17));
getContentPane().add(jl);
and finally the html file with the applet tag:
<APPLET CODE = "test.myapplet" width=760 height=380>
</APPLET>

I have to say that everything works fine even with
long package names besides the loading of the image in
MyClass (in fact you see the JInternalFrame with the
JLabel without icon!). Since I never saw an error in
the Sun Java Console or the DOS window I tried this
last solution, i.e. to shorten the package name. Only
then the icon appears in the label......strange thingsThere shouldn't be a problem with long package (and hence long directory) names.
private String myicon1="images/myimage.gif"; // which becomes the 'path' variable below
BufferedInputStream imgStream = new BufferedInputStream(
myapplet.class.getResourceAsStream(path));So are you sure you are always putting this images subdirectory underneath where your myapplet class lives? If myapplet.class lives in /foo/bar/mypackage, belongs to the 'mypackage' package, and your classpath includes /foo/bar, then your gif file better be at /foo/bar/mypackage/images/myimage.gif (or actually at mypackage/images/myimage.gif from any classpath root)

I really need abstract static methods in abstract class

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