Exception in thread "AWT-EventQueue-0

Question

I am receiving the [Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException] from my code.
a button press triggers this exception, the thing is, the press of the button executes some xqueries and does not have any potential null variables. the variables used on the xquery are taken from a combox and are not null.
the error message iam getting is
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at wizard.Wizard1.jButton2ActionPerformed(Wizard1.java:2915)
        at wizard.Wizard1.access$3400(Wizard1.java:54)
        at wizard.Wizard1$35.actionPerformed(Wizard1.java:2663)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6041)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5806)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4413)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
        at java.awt.Container.dispatchEventImpl(Container.java:2102)
        at java.awt.Window.dispatchEventImpl(Window.java:2440)
        at java.awt.Component.dispatchEvent(Component.java:4243)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)my code on the button is
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                        
        try {
            String minorfunctionality;
            String majorfunctionality;
            String roomstyle;
            String floortype;
            String driver = "org.exist.xmldb.DatabaseImpl";
            Class cl = Class.forName(driver);
            Database database = (Database) cl.newInstance();
            DatabaseManager.registerDatabase(database);
            Collection col = DatabaseManager.getCollection("xmldb:exist://localhost:8080/exist/xmlrpc/db/XMLroom","admin","");          
            XPathQueryService service = (XPathQueryService) col.getService("XPathQueryService", "1.0");
            service.setProperty("indent", "yes");
                XMLResource document = (XMLResource)col.createResource("Example 1", "XMLResource"); 
                String path2= "C:\\Configuration\\XML_29_4_09.xml";
                File f2 = new File(path2);
                if(!f2.canRead()) { 
               System.out.println("cannot read file " + path2 ); 
               return; 
              document.setContent(f2); 
             System.out.print("storing document " + document.getId() + "..."); 
               col.storeResource(document); 
            majorfunctionality = jComboBox1.getSelectedItem().toString();
            minorfunctionality = jComboBox2.getSelectedItem().toString();
            floortype = jComboBox15.getSelectedItem().toString();
            roomstyle = jComboBox3.getSelectedItem().toString();
            ResourceSet result = service.query(" update replace doc('XML_29_4_09.xml')//functionality/MajorFunctionality with <MajorFunctionality>" + majorfunctionality + "</MajorFunctionality>");
            ResourceSet result2 = service.query(" update replace doc('XML_29_4_09.xml')//functionality/MinorFunctionality with <MinorFunctionality>" + minorfunctionality + "</MinorFunctionality>");
            ResourceSet result3 = service.query(" update replace doc('XML_29_4_09.xml')//room/style with <style>" + roomstyle + "</style>");
            ResourceSet result4 = service.query(" update replace doc('XML_29_4_09.xml')//floor/material/texture with <texture>" + floortype + "</texture>");
            ResourceIterator i = result.getIterator();
            while (i.hasMoreResources()) {
            Resource r = i.nextResource();
            System.out.println((String) r.getContent());
        } catch (XMLDBException ex) {
            Logger.getLogger(Wizard1.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            Logger.getLogger(Wizard1.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            Logger.getLogger(Wizard1.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Wizard1.class.getName()).log(Level.SEVERE, null, ex);
    }any ideas why im getting this? thank you in advance.

Answer 1

ok , in line 2915
XPathQueryService service = (XPathQueryService) col.getService("XPathQueryService", "1.0");this declaration is standard when writing an xquery.
and col has been declared before this line
Collection col = DatabaseManager.getCollection("xmldb:exist://localhost:8080/exist/xmlrpc/db/XMLroom","admin","");