Referring a member from static method

Hello,
Suppose I have a class:
public class OuterClass{
public class SomeException{}
public static void someMethod(){
throw new SomeException(); // how to handle this ??
How to handle the creating of an object of the Inner Exception class from within the static method?? Is there any syntax allowing me to do that? Or, I have to declare the SomeException inner class a static class?
Thanks.

Or, I have to declare the SomeException inner class a static class?If your design allows for that, then you should do that anyways - and your problem will be solved - else you need to create an instance of OuterClass on which to create an instance of SomeException

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Accesing database from static method on java collaboration

Hi *,
I want cache data from a oracle database in a java collaboratioon when java collaboration is enabled by emanager.
My java collaboration has a oracleOTD
I did an static method on java collaboration, but I can't access database from static method.
Thanks
Hector

hi hector,
this wont work!
regards chris

Problem with calling dispose() from static method

I have one class, where I have this:
EditorWindow.disposeWindow();and class EditorWindow, where I have static method
protected static void disposeWindow() {
dispose();
}But, dispose() cant be called from static method. Is there any way to hide or close the EditorWindow window?

kaneeec wrote:
I dont have references of these windows, because it would be too difficult. They are created just by new Window().setVisible(true);It's not difficult:
Window w = new Window();
w.setVisible(true);Now you have a reference (w) to your window that you can later call dispose() on.
w.dispose();dispose() isn't a static method, so you have no choice but to call it on a specific instance.

Can't get ClassLoader from static method.

I'm trying to get the ClassLoader within a static method getInstance().
public class PropertyManager {
public static PropertyManager getInstance(String fileName) {
//The following line returns null
ClassLoader cl = (new Object()).getClass().getClassLoader();
URL url = cl.getResource(fileName);
etc...
However if getInstance gets called from e.g. a statless session bean, a null
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The same code executed from a standalone java program (e.g. from
main(String[] args)) returns a valid ClassLoader
Why does getClassLoader behave differently in WebLogic than in a standalone
java program?
Thanks for you help.
Bernie

Sorry for the confusion. I wrote a couple of more test programs and was able
to confirm that WL behaves exacltly the same as java does. For some reason
my intial tests were messed up...
getClassLoader() executed from a static method always returns null (in WL as
well as in a java standalone program).
In this case ClassLoader.getSystemClassLoader() will return a valid class
loader.
Thanks for your help.
Bernie
"Rob Woollen" <[email protected]> wrote in message
news:[email protected]..
Bernhard Lenz wrote:
I tried that as well, but getClassLoader() still returns null when
executed
in WL.
I'm still not clear how getClassLoader() gets affected by running withinWL.
>>
>
Very odd. Where is this class located? in the server's classpath, in ajar or
war file? Does getClass().getClassLoader work from a non-static method inthis
class?
-- Rob
"Rob Woollen" <[email protected]> wrote in message
news:[email protected]..
You want PropertyManager.class.getClassLoader()
-- Rob
Bernhard Lenz wrote:
I'm trying to get the ClassLoader within a static method
getInstance().
>>>>
public class PropertyManager {
public static PropertyManager getInstance(String fileName) {
//The following line returns null
ClassLoader cl = (new Object()).getClass().getClassLoader();
URL url = cl.getResource(fileName);
etc...
However if getInstance gets called from e.g. a statless sessionbean, a
null
is returned instead of a valid ClassLoader.
The same code executed from a standalone java program (e.g. from
main(String[] args)) returns a valid ClassLoader
Why does getClassLoader behave differently in WebLogic than in astandalone
java program?
Thanks for you help.
Bernie

How to use Action listener from Static method

Hello,
I am begginer in Java. I am trying to add JButton and add ActionListener to it in the Java tutorial example (TopLevelDemo).
The problem i am facing are:
1. Since "private static void createAndShowGUI" method is static I cannot reference (this) in the method addActionLisetener when trying to add the JButton
JButton pr = new JButton("Print Report");
     pr.addActionListener(this);
2. If I make "private static void createAndShowGUI" a non static method then it does not run from main method giving me the error(cannot reference non-static).
3. Where do I put actionPerformed method?
I did not post the errors for all situations. Just asking how I can Add JButton and add ActionListener to it in the following code
Thanks
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/* TopLevelDemo.java requires no other files. */
public class TopLevelDemo {
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
private static void createAndShowGUI() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//Create and set up the window.
JFrame frame = new JFrame("TopLevelDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create the menu bar. Make it have a cyan background.
JMenuBar cyanMenuBar = new JMenuBar();
cyanMenuBar.setOpaque(true);
cyanMenuBar.setBackground(Color.cyan);
cyanMenuBar.setPreferredSize(new Dimension(200, 20));
//Create a yellow label to put in the content pane.
JLabel yellowLabel = new JLabel();
yellowLabel.setOpaque(true);
yellowLabel.setBackground(Color.yellow);
yellowLabel.setPreferredSize(new Dimension(200, 180));
//Set the menu bar and add the label to the content pane.
frame.setJMenuBar(cyanMenuBar);
frame.getContentPane().add(yellowLabel, BorderLayout.CENTER);
//Display the window.
frame.pack();
frame.setVisible(true);
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}

Here is one way of doing it...
JButton btn = new JButton("Click on Me");
btn.addActionListener(new ActionListener(){
                          public void actionPerformed(ActionEvent ae){
                            // do something
                            }});here we create an anonymous inner class ActionListener and add it to our button...
- MaxxDmg...
- ' I am not me... '

Static methods in multi-thread environment.

Sorry for this silly question, but I have no clue...
If you're using classes with static methods in a application server environment, would that imply all threads use that same 'one in the jvm' method and would there be a possibility for performance loss?
Is calling another static method from a static method a good idea in a multi-thread environment, with respect to performance? Somehow I seem to get this java.lang.NoClassDefFoundError. Any ideas? The classes are in the same package. I only get these kind of problems calling static methods from static methods in a multi-thread environmnent. The static methods are pure utility functions and of course do not use class state.
Thanks for your help.

Sorry for this question, wasn't thinking straight. I have the answer, won't post question on multiple forums.

Non-static method cannot be referenced from a static context....again sry

Hey, I know you guys have probably seen a lot of these, but its for an assignment and I need some help. The error I'm getting is: non-static method printHistory() cannot be referenced from a static context. Here are the classes effected
public class BankAccount {
private static int nextAccountNumber = 1000;
//used to generate account numbers
private String owner; //name of person who owns the account
private int accountNumber; //a valid and unique account number;
private double balance; //amount of money in the account
private TransactionHistory transactions; //collection of past transactions
private Transaction transaction;
//constructor
public BankAccount(String anOwnerName){
owner = anOwnerName;
accountNumber = nextAccountNumber++;
balance = 0.0;
transactions = new TransactionHistory();
//public String getOwner() {
public void deposit(double anAmount ){
     balance=balance+anAmount;
     transaction=new Transaction(TransactionType.DEPOSIT,accountNumber,anAmount,balance);
     transactions.add(transaction);
//public void withdraw(double anAmount){
//public String toString() {
***public void printHistory(){
     TransactionHistory.printHistory();
AND
public class TransactionHistory {
final static int CAPACITY = 6; //maximum number of transactions that can be remembered
//intentionally set low to make testing easier
private Transaction[] transactions = new Transaction[CAPACITY];
//array to store transaction objects
private int size = 0;
//the number of actual Transaction objects in the collection
public void add(Transaction aTransaction){
     if (size>5){
     transactions[0]=transactions[1];
     transactions[1]=transactions[2];
     transactions[2]=transactions[3];
     transactions[3]=transactions[4];
     transactions[4]=transactions[5];
     transactions[5]=aTransaction;
     transactions[size]=aTransaction;
     size=size++;
public int size() {
     return size;
***public void printHistory() {
     for(int i=0;i<6;i++){
          System.out.println(transactions);
//public void printHistory(int n){
The project still isn't finished, so thats why some code is commented out. The line with *** infront on it are the methods directly effected, I think. Any help would be great.

In Java, static means "something pertaining to an object class". Often, the term class is substituted for static, as in "class method" or "class variable." Non-static, on the other hand, means "something pertaining to an actual instance of an object. Similarly, the term +instance+ is often substituted for +non-static+, as in "instance method" or "instance variable."
The error comes about because static members (methods, variables, classes, etc.) don't require an instance of the object to be accessed; they belong to the class. But a non-static member belongs to an instance -- an individual object. There's no way in a static context to know which instance's variable to use or method to call. Indeed, there may not be any instances at all! Thus, the compiler happily tells you that you can't access an instance member (non-static) from a class context (static).
~

Non-static method close() cannot be referenced from a static context

Friends,
I am having a little help with some static and not static issues.
I created a JMenuBar, it's in the file: SlideViewMenu.java
One of the operations is File->Close and another is File->Exit.
The listener is in the SlideViewMenu.java file. The listener needs to reference two non-static methods within SlideView.java.
Here's some of the code:
SlideViewMenu.java
public class SlideViewMenu {
    public JMenuBar createMenuBar() {
    final Action openAction = new OpenAction();
    Action aboutAction = new AboutAction();
    ActionListener menuListener = new MenuActionListener();
    JMenuBar menuBar = new JMenuBar();
     // All the menu stuff works fine and is taken care of here.
   // Listener for Menu
   class MenuActionListener implements ActionListener {
     public void actionPerformed (ActionEvent actionEvent) {
          String selection = (String)actionEvent.getActionCommand();
         if (selection.equals("Close"))
          SlideViewFrame.close();
         else SlideViewFrame.exit();
}SlideView.java
// Driver class
public class SlideView {
     public static void main(String[] args) {
          ExitableJFrame f = new SlideViewFrame("SlideView");
                // Stuff here, works fine.
// Frame class
class SlideViewFrame extends ExitableJFrame {
        // some things here, work fine.
     private SlideViewMenu menuBar = new SlideViewMenu();
     public SlideViewFrame(String title) {
     // Set title, layout, and background color
     super(title);
     setJMenuBar(menuBar.createMenuBar());
        // Stuff here works fine.
     // Handles doing stuff once the file has been selected
     public void setFileName(File fullFileName, String simpleName) {
        // Stuff here works fine.
     // File->Close. clean up everything.
     public void close() {
          setTitle("SlideView");
          textArea.setText("");
          scrollBar.setVisible(false);
          textArea.setVisible(false);
          statsPanel.setVisible(false);
     // File->Exit.
     public void exit() {
          System.exit(0);
}The error I'm getting is:
SlideViewMenu.java:50: non-static method close() cannot be referenced from a static context
I don't get it?
Thanks for all help.

Making close() and exit() static would not solve the problem because close() requires access to nonstatic member variables/functions.
Fortunately, that is not necessary. The real reason you are having a problem is that you don't have any way in your listener to access the main frame window, which is what the listener trying to control. You made a stab at gaining access by prefixing the function with the class name, but, as the compiler has informed you, that is only valid for static methods. If you think about it, you should see the sense in that, because, what if you had a number of frames and you executed className.close()? Which one would you close? All of them?
Fortunately, there is an easy way out that ties the listener to the frame.
SlideViewMenu.java:public class SlideViewMenu
// Here's where we keep the link to the parent.
private SlideViewFrame parentFrame;
// Here's where we link to the parent.
public JMenuBar createMenuBar(SlideViewFrame linkParentFrame)
    parentFrame = linkParentFrame;
    final Action openAction = new OpenAction();
    Action aboutAction = new AboutAction();
    ActionListener menuListener = new MenuActionListener();
    JMenuBar menuBar = new JMenuBar();
    // All the menu stuff works fine and is taken care of here.
// Listener for Menu --- It is assumed that this is a non-static nested
// class in SlideViewMenu. All SlideViewMenu variables are accessible from
// here. If this is not the case, simply add a similar member variable
// to this class, initialize it with a constructor parameter, and
// pass the SlideViewMenu parentFrame when the listener is
// constructed.
class MenuActionListener implements ActionListener
    public void actionPerformed (ActionEvent actionEvent)
      String selection = (String)actionEvent.getActionCommand();
      // Use parentFrame instead of class name.
      if (selection.equals("Close"))
          parentFrame.close();
        else
          parentFrame.exit();
}SlideView.java// Driver class
public class SlideView
public static void main(String[] args)
    ExitableJFrame f = new SlideViewFrame("SlideView");
    // Stuff here, works fine.
// Frame class
class SlideViewFrame extends ExitableJFrame
// some things here, work fine.
private SlideViewMenu menuBar = new SlideViewMenu();
public SlideViewFrame(String title)
    // Set title, layout, and background color
    super(title);
    //Here's where we set up the link.
    setJMenuBar(menuBar.createMenuBar(this));
// Stuff here works fine.
// Handles doing stuff once the file has been selected
public void setFileName(File fullFileName, String simpleName)
    // Stuff here works fine.
// File->Close. clean up everything.
public void close()
    setTitle("SlideView");
    textArea.setText("");
    scrollBar.setVisible(false);
    textArea.setVisible(false);
    statsPanel.setVisible(false);
// File->Exit.
public void exit()
    System.exit(0);
}

How to invoke a non-static member from a static reference?

Hello JDC
My program consist of several classes. I find it more readable,logic and useful to declare all the methods in all the classes �static� and get access by Class.member().
The problem showed up when I must use a java biuld-in method( as Component.remove ) within my static method , then I receive compile error.
The first alternative is to create the class instance inside the static my static method , the second is to use interface which declare its member as static final. The two ways doesn�t fit to my needs , do anyone know another way?
Thanks in advance
Shay

Hi
im sorry but im not sure what you mean by "OO desgin". i'll appreciate if you'll link me some sources about this , its sound very interesting .
It may be that you are moving to Java from COBOL or >FOTRAN or something and you are not comfortable with >OO philosophy
For example, you can never have two instances of >the same class have different properties. What's the >point of having classes at all if you are going to do it >this way? Java is my first language , you sound very unhappy about the way i ignore the OOP , i think you right in some terms but i need to exam my thinking again and think how can i implements the same ideas in a form of OOP. whenever all those information will come i'll be able to response.
thanks for your reply
Shay Gaghe

Are DLL methods called as instance or static methods from Java ?

Hi,
I have only a small question.
When I call a C++ DLL method from Java using JNI, do I instantiate it like an object method or is it called as a static method ?
I am asking you this because I will use servlets (Java 1.2.2) to call a DLL. These servlets may run concurrently in any moment, and I pass some data to this DLL. I want to know if there is any possibility of this data becoming corrupt, because of one concurrent servlet rewriting the data another servlet has passed.
Thanks and regards.

The question is not specific enough.
Methods in C/C++ can be qualified with the following forms:
-global (C/C++)
-static member(C++ class method)
-instance member(C++ class method)
Since you didn't provide your code I couldn't possible determine which of the above you are using, but presumably you know.
On the other hand a java native method is either static or non-static depending on how you defined it in the class. Once again without the code there is no way to say and presumably you already know this.
The context of the methods is the same context that a similar servlet method has. But naturally in C/C++ is is easy to circumvent the context - for example by using a global variable.
Data in C/C++ can always become corrupt and in the vast (all?) cases it is because something is wrong in the C/C++ code. Like a pointer that is not initialized, or a pointer used after it is free'd. Or writing past the end of a buffer, or writing before the beginning of a buffer.

Calling non-static command from within static method

Hello,
I have a static method that reads bytes from serial port, and I want to set a jTextField from within this method. but I get error that says it is not possible to call non static method from a static one. How can it be solved?

ashkan.ekhtiari wrote:
No, MTTjTextField is the name of jTextFiled class instance.You haven't declared any such variable in the class you posted, not to mention that such a variable name violates standard code conventions.
This is and instance of that object actually. You haven't declared any such variable in the class you posted.
the problem is something else. No, it isn't, based on the information you have provided. If you want accurate guidance, don't post misleading information about your problem.
It can not be set from within static method.A question commonly asked on Java forums concerns an error message similar to the following:
non-static variable cannot be referenced from a static context
In Java, static means "something pertaining to an object class". Often, the term class is substituted for static, as in "class method" or "class variable." Non-static, on the other hand, means "something pertaining to an actual instance of an object. Similarly, the term instance is often substituted for non-static, as in "instance method" or "instance variable."
The error comes about because static members (methods, variables, classes, etc.) don't require an instance of the object to be accessed; they belong to the class. But a non-static member belongs to an instance -- an individual object. There's no way in a static context to know which instance's variable to use or method to call. Indeed, there may not be any instances at all! Thus, the compiler happily tells you that you can't access an instance member (non-static) from a class context (static).
Once you understand this concept, you can fix your own problem.
~

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!

How to call a static method from an event handler

Hi,
I'm trying to call a static method of class I designed. But I don't know how to do it. This method will be called from an event handler of a web dynpro for Abap application.
Can somebody help me?
Thx in advance.
Hamza.

To clearly specify the problem.
I have a big part code that I use many times in my applications. So I decided to put it in a static method to reuse the code. but my method calls functions module of HR module. but just after the declaration ( at the first line of the call function) it thows an exception. So I can't call my method.

Calling a method from a static method

hello all,
I'm calling a non-static method from a static method (from the main method). To overcome this i can make the method i am calling static but is there another way to get this to work without making the method that is being called static?
all replies welcome, thanks

When you call a non-static method, you are saying you are calling a method on an object. The object is an instance of the class in which the method is defined. It is a non-static method, because the instance holds data in it's instance variables that is needed to perform the method. Therefore to call this kind of method, you need to get (or create an instance of the class. Assuming the two methods are in the same class, you could do
public class Foo
     public static void main(String[] args)
            Foo f = new Foo();
            f.callNonStaticMethod();
}for instance.

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!

Referring a member from static method

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