NullPointerException in JComboBox.removeAllItems();

Question

I want to remove all items in JComboBox to update button.

This method is use to get suppliers' names at the program start:

private void fillCmbOrderSupplyer() {
    try {
        DataOb.dbConnects();
        System.out.println("Database connection success...");
        res = DataOb.viewAll(dbSupp);
        //o_cmbSupplyer.addItem("Select supplyer");
        
        while (res.next()) {
            String name = res.getString("SName");
            o_cmbSupplyer.addItem(name);
        }

    } catch (Exception ex) {
        System.out.println(ex);

    }
}

and this code is used to remove all items in the combo box, and the next line gets suppliers' names again:

o_cmbSupplyer.removeAllItems();
fillCmbOrderSupplyer();

This is the error message at o_cmbSupplyer.removeAllItems();

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at computer.sales.system.Inventory.o_cmbSupplyerActionPerformed(Inventory.java:4500)
    at computer.sales.system.Inventory.access$5600(Inventory.java:39)
    at computer.sales.system.Inventory$61.actionPerformed(Inventory.java:2125)
    at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1258)
    at javax.swing.JComboBox.contentsChanged(JComboBox.java:1332)
    at javax.swing.JComboBox.intervalRemoved(JComboBox.java:1352)
    at javax.swing.AbstractListModel.fireIntervalRemoved(AbstractListModel.java:179)
    at javax.swing.DefaultComboBoxModel.removeAllElements(DefaultComboBoxModel.java:174)
    at computer.sales.system.Inventory.jButton22ActionPerformed(Inventory.java:3777)
    at computer.sales.system.Inventory.access$2400(Inventory.java:39)
    at computer.sales.system.Inventory$26.actionPerformed(Inventory.java:1259)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
    at java.awt.Component.processMouseEvent(Component.java:6539)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6304)
    at java.awt.Container.processEvent(Container.java:2239)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2297)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
    at java.awt.Container.dispatchEventImpl(Container.java:2283)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
    at java.awt.EventQueue$4.run(EventQueue.java:733)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

I tried this code and it gives the same error:

DefaultComboBoxModel o_cmbSupp = (DefaultComboBoxModel) o_cmbSupplyer.getModel();

o_cmbSupp.removeAllElements();
fillCmbOrderSupplyer();

nullpointer exception... at this point it probably means your combobox is null and not instantiated, or you have nothing / null to add to your combobox. — YHStan, Jun 21 '21 at 13:09

NullPointerException in JComboBox.removeAllItems();

0 Answers0