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Null Object EXCEPTION

i will give you an example of my class because it is big:
public class test{

private Data data;

public test()[
}

public void createData(){
data = new data();
setData(data)
getData().createTable();
}

public void removeRow(){
// THE EXCEPTION IS HAPPENING IN HERE GETDATA() IS GIVING ME A NULL POINTER WHY?
// AND IT IS ALREADY INITIALIZED!!!
JTabee table = getData().gettable();
}

public void setData(data){
this.data = data;
}

public void getData(){
return this.data;
}

To what do you assign 'table' ? - i see nothing

ASKER

i am assigning table to JTable table = getData().getTable();

public class Data{
private JTable table;
//code...
public setTable(table){
this.table = table;
}

public getTable(){
return this.table;
}
}

So i am getting Table in class test and assining table in this class to table from class Data.

ASKER

the problem is that once
public void createData(){
data = new data();
setData(data)
getData().createTable();
}

GetData() becomes NULL; why? it is initialized in this function and i used setData

>>
data = new data();
setData(data)
getData().createTable();
>>

>>JTabee table = getData().gettable();

Is what you posted earlier - no table get create and assigned that i can see

ASKER

once i leave this method createData() getData becomes null when i use it in other methods.

ASKER

JTabee table = getData().gettable();
I want to Get JTable table from Class Data.
and assign Table in class test to table of class Data.
what is the problem why it isn't working?

ASKER

The Problem is not with Table is with getData() it is becoming Null each time

ASKER

i will make it more simple:
in class test

i have private Data data;

in method BLABLABLA(){
data = new Data();
setData(data);
getData();
// in here getData() is not null
}

once it is used in another method it becomes null!!!!

ASKER

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

where is your main() method? do you call createData() before you call removeRow()?

ASKER

i am using Listeners
i have a button at first i click on like Open.
it calls method CreateData().
so data shouldn't be null cos it is intilializes in this method createData() correct?

once i click on removeRow() method and call getData() from the same class test.
i receive this Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

if i do system.out.print(getData()) i have NULL on the screen the object becomes null!

can i see your actionPerformed() method?

>>once it is used in another method it becomes null!!!!

It will become null if you replace the original reference to 'data' with another, local, one and then try to read it again once you're out of the local context (method)

ASKER

this is the class:
public class MenuOperation extends JFrame implements ActionListener{

private MenuTabs tabs;
private File f;
private Data data;

/** Creates a new instance of MenuOperation */
public MenuOperation(){

}

public void actionPerformed(ActionEvent e) {
String actionCommande = e.getActionCommand();

if(actionCommande.equals("Importer Fichier..." )){
ouvrir();
}else if(actionCommande.equals("Supprimer Colonne")){
selectionnerColonne();
}

// IN THIS METHOD I DO SETDATA()
private void ouvrir(){
JFileChooser jfc = new JFileChooser();
Container c=InfoInterface.getDonnees().getC();

jfc.setCurrentDirectory(new File("."));
jfc.addChoosableFileFilter(new FiltreExtension("xls", "Fichier EXCEL"));
jfc.addChoosableFileFilter(new FiltreExtension("xml", "Fichier XML"));
jfc.addChoosableFileFilter(new FiltreExtension("tree", "Fichier Regress"));
int resultat = jfc.showOpenDialog(this);

if(resultat == JFileChooser.CANCEL_OPTION){

return;

}else if(resultat == JFileChooser.APPROVE_OPTION){

f = jfc.getSelectedFile();
String extension = Extension.getExtension(f);
cd = new ChargementDonnees(f);
setData(new Data());
getData().creerTable(cd);
cn = new ChargementNature(getData());
setNature(new Nature());
getNature().creerTable(cn);
tabs = new MenuTabs();
tabs.ajoutTab(getNature(), "nature");
PanelPrincipale panel = new PanelPrincipale(getData(), tabs);
c.removeAll();
c.add(panel);
c.validate();

}
}

// in this method getData() becomes null
private void selectionnerColonne() {
supprimerColonne(getData().getTable(),
getData().getTable().getColumnModel().getSelectionModel().getLeadSelectionIndex());
}

public Data getData() {
return data;
}

public void setData(Data data) {
this.data = data;

}
}

ASKER

what should i do then if it becomes null outside i need to use it in all the methods

ASKER

data should be used in all the methods. i can't each time create a new one.

ASKER

can i use inheritence? is it possible to make it extends Data?

where is your object of class test? you to call setData() and getData from the same test object.

ASKER

ignore the last message.
YEs setData and getData are called from the same class test

they're in the same class, but i don't see a common object of that class that is calling both methods

ASKER

what do you mean? i don't understand you.

ASKER

setData(new Data());
it is initialized
in method createTable();

and in method supprimerColonne(){
// getData() becomes null
}

ASKER

createTable(){
setData(new Data());
getData().creerTable(cd);
}
no problem in method createTable();

in the other methods it becomes null what should i do?

I mean that you should something like:

test t = new test();

... some code

t.setData(new Data());

... some code

JTable table = t.getData().gettable();

In the stack trace of the exception, you should see a line number. Please point to that line in the code

ASKER

Imagine this class:

class test{
private Data data;

public void initData(){
setData(new Data());
getData(); // fine in here
}

public void blabla(){
getData() = null;// why?
}

setData(){
bla bla}
getData{return data}

ASKER

in class test i must create object test?

ASKER

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Utilites.MenuOperation.selectionnerColonne(MenuOperation.java:159)
at Utilites.MenuOperation.actionPerformed(MenuOperation.java:58)
i didn't give you the whole Code it is so big.

ASKER

setData and getData are in class Test is it possible to create object test in class test?

no, but you're using the methods in another class, right? so you must have a test object there.

ASKER

no no both setData and getData are in class test.
so i used getData() to get method getTable() from class Data

Both Methods are in the same class Test.
Look at that example please
class test{
private Data data;

public void initData(){
setData(new Data());
getData(); // fine in here
}

public void blabla(){
getData() = null;// why?
}

setData(){
bla bla}
getData{return data}

In selectionnerColonne, split those references up. You call the same method repeatedly unnecessarily anyway. Start with

Data data = getData(); //test this
JTable table = data.getTable(); // and this

never mind about what i was saying; i didn't notice that you also had getData() and setData() methods in class MenuOperation.

put a System.out.println() statement after this if statement in your code.

else if(resultat == JFileChooser.APPROVE_OPTION){

make sure that that if is evaluating true

ASKER

private void selectionnerColonne() {
Data data = getData(); //test this
JTable table = data.getTable(); // and this

didn't work i am always getting an exception NullExceptionPointer

ASKER

else if(resultat == JFileChooser.APPROVE_OPTION){

f = jfc.getSelectedFile();
String extension = Extension.getExtension(f);
cd = new ChargementDonnees(f);
setData(new Data());
getData().creerTable(cd);
cn = new ChargementNature(getData());
setNature(new Nature());
getNature().creerTable(cn);
tabs = new MenuTabs();
tabs.ajoutTab(getNature(), "nature");
PanelPrincipale panel = new PanelPrincipale(getData(), tabs);
c.removeAll();
c.add(panel);
c.validate();
System.out.println("test") ;
}

it worked i have test on the screen

ASKER

data is in the class and it is initialized what is the problem? mmm weird

try changing your setData() method as follows

public void setData(Data d) {
data = d;

}

ASKER

i did but it is the same anyway it wont change.
But is it possible that an object becomes null after it has been created?

>>didn't work i am always getting an exception NullExceptionPointer

It's not intended as a solution - it's to isolate the problem. Which object is null?

also, can i see how you add your ActionListeners?

ASKER

JTable table = data.getTable(); // and this

in here data is null;

ASKER

well they are called from another class
where i do like that:
private MenuOperation menuOperation = new MenuOperation();
menuItem.addActionListener(menuOperation);

ASKER

i don't think that it is the problem.

SOLUTION

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looks more likely that your problem is is in your Data class, can u post that.
check that it contains a correct table instance.
You may be creating a new Data instance and not setting its table

ASKER

ok
public class Data extends JPanel{

private JTable table;
private TableModel model;
private static boolean availabe;
private ChargementDonnees donnees;

/**
* Copy constructeur
* @param _donnees Donnees est un parametre envoyer par la classe ChargementDonnees
* qui prend les donnees d'un fichier Excel.
*/

public Data(){
super();
setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
}

public void creerTable(ChargementDonnees donnees){
setAvailabe(true);
this.setDonnees(donnees);
setTable(new JTable(getDonnees()));
table.setRowSelectionAllowed(false);
table.setColumnSelectionAllowed(false);
TableColumnModel tcm = table.getColumnModel();
JScrollPane jsp = new JScrollPane(getTable());
JViewport jvp = new JViewport();
jvp.setView(new RowNumberHeader(getTable()));
jsp.setRowHeader(jvp);
add(jsp,BorderLayout.CENTER);

}

/**
* retourne un objet JTable
* @return retourne table
*/
public JTable getTable() {
return table;
}

/**
* ajouter un objet Table
* @param aTable pour ajouter une table
*/

public static boolean isAvailabe() {
return availabe;
}

public static void setAvailabe(boolean aAvailabe) {
availabe = aAvailabe;
}

public ChargementDonnees getDonnees() {
return donnees;
}

public void setDonnees(ChargementDonnees donnees) {
this.donnees = donnees;
}

public void setTable(JTable table) {
this.table = table;
}
}

SOLUTION

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ASKER

Yes i always pass the same object.

ASKER

Well because class MenuOperation is supposed to handle the actions. this is why

> getData().getTable().getColumnModel().getSelectionModel().getLeadSelectionIndex());

u could also possible have no selection, try the following so you can see whats happening

System.out.println("data="+getData());
System.out.println("table="getData().getTable());
System.out.println("columns="+getData().getTable().getColumnModel());
System.out.println("selection="+getData().getTable().getColumnModel().getSelectionModel);
getData().getTable().getColumnModel().getSelectionModel().getLeadSelectionIndex());

can you post the whole stack trace?

System.out.println("data="+getData());
System.out.println("table="getData().getTable());
System.out.println("columns="+getData().getTable().getColumnModel());
System.out.println("selection="+getData().getTable().getColumnModel().getSelectionModel);
supprimerColonne(getData().getTable(),
getData().getTable().getColumnModel().getSelectionModel().getLeadSelectionIndex());

ASKER

private void selectionnerColonne() {

System.out.println("data="+getData());
System.out.println("table="+getData().getTable());
System.out.println("columns="+getData().getTable().getColumnModel());
System.out.println("selection="+getData().getTable().getColumnModel().getSelectionModel());

Data data = this.getData();
JTable table = data.getTable();

supprimerColonne(table,
table.getColumnModel().getSelectionModel().getLeadSelectionIndex());
}

stackTrace:
compile:
data=null
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Utilites.MenuOperation.selectionnerColonne(MenuOperation.java:161)
at Utilites.MenuOperation.actionPerformed(MenuOperation.java:58)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
at javax.swing.AbstractButton.doClick(AbstractButton.java:302)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1000)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1041)
at java.awt.Component.processMouseEvent(Component.java:5488)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3126)
at java.awt.Component.processEvent(Component.java:5253)
at java.awt.Container.processEvent(Container.java:1966)
at java.awt.Component.dispatchEventImpl(Component.java:3955)
at java.awt.Container.dispatchEventImpl(Container.java:2024)
at java.awt.Component.dispatchEvent(Component.java:3803)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3892)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)
at java.awt.Container.dispatchEventImpl(Container.java:2010)
at java.awt.Window.dispatchEventImpl(Window.java:1778)
at java.awt.Component.dispatchEvent(Component.java:3803)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)
debug:
BUILD SUCCESSFUL (total time: 12 seconds)

ASKER

it is not passing data

And are you sure ouvrir() gets called *before* actionPerformed()

sorry meaqnt, before selectionnerColonne()

ie. that the chooser action runs first

Make sure the reference to a valid instance is not getting lost with your gui when you remove stuff from it

ASKER

well yes first i call ouvrir then i call selectionnerColonne()
it is possible that the error is in the design?

> data=null

that suggestes your ouvrir() has not got executed beforehand as I mentioned above

to safeguard against that use:

if (getData()!=null) {
supprimerColonne(getData().getTable(),
getData().getTable().getColumnModel().getSelectionModel().getLeadSelectionIndex());
}

ASKER

but i mean when i call ouvrir() get the table in front of me
do you think that inserrercolonne() is being executed before it?

Add the follwoing to check its getting called:

System.out.println("Opening dialog");
int resultat = jfc.showOpenDialog(this);
System.out.println("ooption="+resultat);

if(resultat == JFileChooser.CANCEL_OPTION){

return;

}else if(resultat == JFileChooser.APPROVE_OPTION){

System.out.println("APPROVED");
...

> do you think that inserrercolonne() is being executed before it?

what you have posted suggests that,

*or* you are creating two instances on MenuOperation.

ASKER

compile:
Opening dialog
ooption=0
APPROVED

ASKER

option = 0
if result = 0 is that a problem?

it can't be, because it printed "APPROVED"

ASKER

i think that i will have to design the application again.

SOLUTION

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ASKER

is there a way to post my application so that you can check it?
post the whole code

can you post your gui class?

ASKER

yes well i will explain it. i created ItemMenu and MenuOutils to be able to create Menu items
dynamically i think that this is the problem.

// This is the main class
public class Donnees extends JFrame {

// private JFrame frame = new JFrame();
private JMenuBar menuBar;
private Container c;

// Constructeur de la classe Donnees
public Donnees(){
super("Regression:Menu Principal");
setC(getContentPane());

}
// Methode pour initialize la fenetre principale
public void initialization(){

// Appelle WindowListener pour fermer la Fenetre
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent evt) {
exitForm(evt);
}
});

// Creation de la barre Menu

menuBar = new JMenuBar();
// Menu Principale
MenuOutils m;
ItemMenu mi;

//Menu Fichier
m = new MenuOutils("Fichier",'f');
menuBar.add(m.initialize());
mi = new ItemMenu("Importer Fichier...");
m.ajouter(mi.initializer());
m.Separateur();
mi = new ItemMenu("Enregistrer sous...");
m.ajouter(mi.initializer());
m.Separateur();
mi = new ItemMenu("Nouveau...");
m.ajouter(mi.initializer());
mi = new ItemMenu("Quitter",'q',KeyStroke.getKeyStroke(
KeyEvent.VK_Q,ActionEvent.CTRL_MASK
));
m.ajouter(mi.initializer());

// Menu Edition
m = new MenuOutils("Edition",'e');
menuBar.add(m.initialize());
mi = new ItemMenu("Inserrer Colonne");
m.ajouter(mi.initializer());
mi = new ItemMenu("Supprimer Colonne");
m.ajouter(mi.initializer());
m.Separateur();
mi= new ItemMenu("Inserrer Ligne");
m.ajouter(mi.initializer());
mi = new ItemMenu("Supprimer Ligne");
m.ajouter(mi.initializer());
m.Separateur();
mi = new ItemMenu("Copier",'o',KeyStroke.getKeyStroke(
KeyEvent.VK_C,ActionEvent.CTRL_MASK
));
m.ajouter(mi.initializer());
mi = new ItemMenu("Couper",'c',KeyStroke.getKeyStroke(
KeyEvent.VK_X,ActionEvent.CTRL_MASK
));
m.ajouter(mi.initializer());
mi = new ItemMenu("Coller",'o',KeyStroke.getKeyStroke(
KeyEvent.VK_V,ActionEvent.CTRL_MASK
));
m.ajouter(mi.initializer());

// Menu Analyse
m = new MenuOutils("Analyse",'a');
menuBar.add(m.initialize());
mi = new ItemMenu("Stat Description");
m.ajouter(mi.initializer());
m.Separateur();
mi = new ItemMenu("Methode 1");
m.ajouter(mi.initializer());
mi = new ItemMenu("Methode 2");
m.ajouter(mi.initializer());

// Menu Aide
m = new MenuOutils("?",'?');
menuBar.add(m.initialize());
mi = new ItemMenu("Version");
m.ajouter(mi.initializer());
m.Separateur();
mi = new ItemMenu("Aide");
m.ajouter(mi.initializer());
setJMenuBar(menuBar);
}

// Methode pour quitter l'application
private void exitForm(WindowEvent e) {
int reponse = JOptionPane.showConfirmDialog(null,
"Voulez vous quitter?", "quitter", JOptionPane.YES_NO_OPTION);
if(reponse== JOptionPane.YES_OPTION) {
dispose();
System.exit(0);
}else{
return;
}
}

public Container getC() {
return c;
}

public void setC(Container c) {
this.c = c;
}

}

and this is where i assign an action listener:
public class ItemMenu extends JMenuItem {
private String nom;
private int nemonic;
private KeyStroke key;
private JMenuItem menuItem;

private MenuOperation menuOperation = new MenuOperation();

/**
* Creates a new instance of ItemMenu
*/
public ItemMenu(String _nom,int _nemonic,KeyStroke _key) {
this.setNom(_nom);
this.setNemonic(_nemonic);
this.setKey(_key);
}

public ItemMenu(String _nom) {
this.setNom(_nom);
}

public JMenuItem initializer(){

menuItem = new JMenuItem(getNom());
menuItem.setMnemonic(Integer.valueOf(getNemonic()));
menuItem.setAccelerator(getKey());
menuItem.addActionListener(menuOperation);
return menuItem;
}

public String getNom() {
return nom;
}

public void setNom(String nom) {
this.nom = nom;
}

public int getNemonic() {
return nemonic;
}

public void setNemonic(int nemonic) {
this.nemonic = nemonic;
}

public KeyStroke getKey() {
return key;
}

public void setKey(KeyStroke key) {
this.key = key;
}

}

so i created an object in class Donnees like mi and give it an actionListener

ASKER

i wanted menu items to be added dynamically. it is a nice way but you are right the problem is there i think.

you are create multiple instance of MenuOperation, that's the problem

ASKER

please can you explain more where do you mean i am creating them?
please. i am lost

move these statements out into your gui class:

MenuOperation menuoperation = new MenuOperation();

menuitem.addActionListener(menuoperation);

ASKER CERTIFIED SOLUTION

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SOLUTION

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ASKER

ok i will try it. it is late now it is 1:30 AM working all day.
it is possible to post tomorrow what i tried ?
so that you can comment please?

yes, of course.

ASKER

IT WORKED!!!!!!!!!!!!!!!! YOU ARE GREAT PEOPLE THANK YOU SOO MUCH!!!!!!!!!!

ASKER

thank you all!!

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ASKER

mm guess that you all deserve gee mmmmmmmmmmmm

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ASKER

don't know how to split the points you all deserve 500