Question

I am having issues with the initVectors during table update. It throws a NullPointerException.

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at HardwareDbFile.HardwareInventoryUI.update(HardwareInventoryUI.java:47)
    at java.util.Observable.notifyObservers(Observable.java:159)
    at java.util.Observable.notifyObservers(Observable.java:115)
    at HardwareDbFile.HardwareFileWatchdog.actionPerformed(HardwareFileWatchdog.java:36)
    at javax.swing.Timer.fireActionPerformed(Timer.java:312)
    at javax.swing.Timer$DoPostEvent.run(Timer.java:244)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
    at java.awt.EventQueue.access$000(EventQueue.java:101)
    at java.awt.EventQueue$3.run(EventQueue.java:666)
    at java.awt.EventQueue$3.run(EventQueue.java:664)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

TableModel

package HardwareDbFile;



import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.util.Vector;
import javax.swing.table.AbstractTableModel;


public class HardwareFileTableModel extends AbstractTableModel{
    protected Vector data;
    protected Vector columnNames ;
    protected String datafile;

    public HardwareFileTableModel(String file){
        datafile = file;
        initVectors();  
    }

    public void initVectors() {
        String aLine ;
        data = new Vector();
        columnNames = new Vector();
        try {
            FileInputStream fin =  new FileInputStream(datafile);
            try (BufferedReader br = new BufferedReader(new InputStreamReader(fin))) {
                StringTokenizer st1 = new StringTokenizer(br.readLine(), "|");
                while(st1.hasMoreTokens()) {
                    columnNames.addElement(st1.nextToken());
                }
                // extract data
                while ((aLine = br.readLine()) != null) {
                    StringTokenizer st2 = new StringTokenizer(aLine, "|");
                    while(st2.hasMoreTokens()) {
                        data.addElement(st2.nextToken());
                    }
               }
           }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
    @Override
    public int getRowCount() {
        return data.size() / getColumnCount();
    }

    @Override
    public int getColumnCount(){
        return columnNames.size();
    }

    @Override
    public String getColumnName(int columnIndex) {
        String colName = "";

        if (columnIndex <= getColumnCount()) {
            colName = (String)columnNames.elementAt(columnIndex);
        }
        return colName;
    }

    @Override
    public Class getColumnClass(int columnIndex){
        return String.class;
    }

    @Override
    public boolean isCellEditable(int rowIndex, int columnIndex) {
        return false;
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        return (String)data.elementAt( (rowIndex * getColumnCount()) + columnIndex);
    }

    @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
    }
}

Observer Class

package HardwareDbFile;


import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.Timer;

 public class HardwareFileWatchdog extends Observable implements ActionListener {
     Timer time = new Timer(1000,this); // check every second
     long lastModified;
     String file;

     HardwareFileWatchdog (String string) {
         file = string;
         File f = new File(file);
         lastModified = f.lastModified(); // original timestamp
         time.start();
    }

    @Override
     public void actionPerformed(ActionEvent e) {
         File f = new File(file);
         long actualLastModified = f.lastModified() ;
         if (lastModified != actualLastModified) {
             // the file have changed
             lastModified = actualLastModified;
             setChanged();
             notifyObservers();
         }
     }
}

Main Class snippet

    public class HardwareInventoryUI extends javax.swing.JFrame implements Observer {

    private String datafile = "hardware.dat";
    private String dataFilePath = "C:\\Windows\\Temp\\hardware.dat";
    protected HardwareFileTableModel model;

    /**
    * Creates new form HardwareInventoryUI
    */
    public HardwareInventoryUI() {
        initComponents();

        HardwareFileWatchdog  fileWD;
        Font font;
        font = new Font("SanSerif",Font.PLAIN,14);
        setFont(font);

        // this watchdog (an Observable object) is monitoring any file change
        fileWD = new HardwareFileWatchdog(dataFilePath);
        fileWD.addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        // reload data because data file have changed
        model.initVectors();
        jTable.repaint();
    }

Button Action to add record

    private void jAddRecordActionPerformed(java.awt.event.ActionEvent evt) {

        String toolID = jToolID.getText();
        String toolName = jToolName.getText();
        String quantity = jQuantity.getText();
        String itemPrice = jItemPrice.getText();
        try {
            FileWriter fstream = new FileWriter(dataFilePath, true);
            BufferedWriter newRecord = new BufferedWriter(fstream);
            newRecord.newLine();
            newRecord.write(toolID + "|"+ toolName + "|" + quantity + "|" + itemPrice );
            newRecord.close();
        } catch (IOException ex) {
            Logger.getLogger(HardwareInventoryUI.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

Process: file is created and loaded in the table model, which works fine. The problem comes when I attempt to add a new record. The record is added to the text file in proper format, but it throws an exception during the attempt to update the table model with the new data. I am at a loss.

Answer 1

model is null. You have not created an instance for it.