Question

I am trying to build a simple gui program. Everything worked well because I tested the classes before adding some GUI components such as in SWING and AWT. However when I tried some input and press the submit button it gives me this error.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.simpleAccountEntry.SimpleAccountListener.actionPerformed(SimpleAccountListener.java:15)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2012)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2335)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:404)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6389)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3268)
    at java.awt.Component.processEvent(Component.java:6154)
    at java.awt.Container.processEvent(Container.java:2045)
    at java.awt.Component.dispatchEventImpl(Component.java:4750)
    at java.awt.Container.dispatchEventImpl(Container.java:2103)
    at java.awt.Component.dispatchEvent(Component.java:4576)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4633)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4297)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4227)
    at java.awt.Container.dispatchEventImpl(Container.java:2089)
    at java.awt.Window.dispatchEventImpl(Window.java:2518)
    at java.awt.Component.dispatchEvent(Component.java:4576)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:672)
    at java.awt.EventQueue.access$400(EventQueue.java:96)
    at java.awt.EventQueue$2.run(EventQueue.java:631)
    at java.awt.EventQueue$2.run(EventQueue.java:629)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:116)
    at java.awt.EventQueue$3.run(EventQueue.java:645)
    at java.awt.EventQueue$3.run(EventQueue.java:643)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:642)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)

I tried to debug it since yesterday but I couldn’t find where I made a mistake. I tried to check this error code:

 com.simpleAccountEntry.SimpleAccountListener.actionPerformed(SimpleAccountListener.java:15)

and it points to this class:

public class SimpleAccountListener implements ActionListener{

    private SimpleAccountActionsPanel listen;
    
    public SimpleAccountListener(SimpleAccountActionsPanel functionPanel){
        listen = functionPanel;
    }
    
    public void actionPerformed(ActionEvent e){
        listen.recordPatient(); //SimpleAccountListener.java: 15
    }
}

listen.recordPatient() can be found in this class along with other methods I have written

EDIT

 public class SimpleAccountActionsPanel extends JPanel{
    
        private SimpleAccountPanel account = new SimpleAccountPanel();
**//Initialize this line
        static private SimpleAccountActionsPanel perform = new SimpleAccountActionsPanel();**
        
        private DetailsEntry<Details> setPatient = new DetailsEntry<Details>();
        
        static private JButton submit;
        static private JButton delete;
        
        public SimpleAccountActionsPanel(){
            this.setLayout(new GridLayout(1,2));
                                                                                        
            
            submit = new JButton("Submit Entries");
            delete = new JButton("Delete Entries");
            
            submit.setBackground(Color.DARK_GRAY);
            submit.setForeground(Color.ORANGE);
            
            delete.setBackground(Color.DARK_GRAY);
            delete.setForeground(Color.ORANGE);
            
            this.add(submit);
            this.add(delete);
            
            //SimpleAccountPanel varFields = new SimpleAccountPanel();
            SimpleAccountListener performFn = new SimpleAccountListener(perform);
            submit.addActionListener(performFn);
        }
        
        public void recordPatient(){
            String name = account.getEnterName().getText();
            String dob = account.getEnterDOB().getText();
            String doc = account.getEnterDr().getText();
            String allergy = account.getAllergies().getText();
            String room = account.getEnterRoomNo().getText();
            int convRoom = Integer.parseInt(room);
            
            setPatient.addEntry(new Details(name, dob, doc, allergy, convRoom));
        }
    }

Anyone care to help me out? If you need more of the classses I implemented I can post it just let me know Thanks in advance.

EDIT

Thanks to Max and MadProgrammer I initialized perform as suggested program now works perfectly.

Answer 1

You’re passing SimpleAccountListener a reference to the variable perform which isn’t initialised in the constructor of SimpleAccountActionsPanel, hence the NPE

SimpleAccountListener performFn = new SimpleAccountListener(perform); // <-- perform is not initialised...

I’m trying to figure out why you didn’t just pass this?

SimpleAccountListener performFn = new SimpleAccountListener(this);