Cant delete or add item to Jlist as nthing happens

Question

Hi all,
regarding the first part where pass of string array into object array. I have done it (thanks again for the help). But regarding the add and remove elements from the Jlist cant be done.. below is my code for the delete button when press. I cast it into int for the ManualList.getSelectedIndex();(at part A) but cant display and keep having a error call
java.lang.NullPointerException at ManualChange&ValueReporter.valueChanged
code for value reporter is at part B
Part A
private void deleteMouseClicked(MouseEvent e)
int n =(int)ManualList.getSelectedIndex();
if (!(n < 0) || (n > listModel.size()))
listModel.remove(n);
delete.setEnabled(false);
ManualList.repaint();
ManualList.revalidate();
Part B
private class ValueReporter implements ListSelectionListener {
public void valueChanged(ListSelectionEvent event) {
// if (!event.getValueIsAdjusting())
// gettext.setText(ManualList.getSelectedValue().toString());
ManualList.repaint();
ManualList.revalidate();
Any help is greatly appreciated.
alright, i redo part A the code is shown below but i still cant get the display out.
Is there some problem in my code? or is the repaint and revalidate thing wrong usage here ? Need help regarding this. Thanks
int n =ManualList.getSelectedIndex();
if (!(n < 0) || (n > listModel.size()))
listModel.removeElement(arrayObject[n]);
delete.setEnabled(false);
ManualList.repaint();
ManualList.revalidate();

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.awt.event.MouseEvent.*;
import javax.swing.event.*;
import java.io.*;
import javax.swing.DefaultListModel.*;
import java.util.Properties;
import java.util.ArrayList;
    public class smallProgram extends JFrame //implements ListSelectionListener
        JPanel p;
    private DefaultListModel listModel;
     JLabel ManualJob = new JLabel();
     JTextField gettext  = new JTextField();
     JScrollPane scrollPane1 = new JScrollPane();
     JButton okButton = new JButton();
     JButton cancelButton = new JButton();
     JButton add = new JButton();
     JButton delete = new JButton();
     JList ManualList;
     int tokenNo;
     String real,ss;
     String[] values;
     Object[] arrayObject;
     java.util.StringTokenizer tokenizer;
     BufferedReader in;
     ArrayList data;
     public static void main(String args[])
         new smallProgram();
      public smallProgram()
            setTitle("Small Program");
            p = (JPanel) this.getContentPane();
            p.setLayout(null);
            setSize(515, 585);
            setVisible(true);
           //---- ManualJob ----
           ManualJob.setText("Manual Jobs Classification");
           ManualJob.setFont(new Font("Times New Roman", Font.BOLD, 14));
           p.add(ManualJob);
           ManualJob.setBounds(10, 435, 190, 35);
           setVisible(true);
           //---- gettext ----
           gettext.setFont(new Font("Times New Roman", Font.PLAIN, 12));
           p.add(gettext);
           gettext.setBounds(365, 435, 115, 25);
           setVisible(true);
           //Buttons for add, del, ok and cancel
           //---- Add ----
           add.setText("Add");
           add.addMouseListener(new MouseAdapter() {
               @Override
               public void mouseClicked(MouseEvent e) {
                   addMouseClicked(e);
           p.add(add);
           add.setBounds(355, 485, 60, add.getPreferredSize().height);
          //---- delete ----
           delete.setText("Delete");
           delete.addMouseListener(new MouseAdapter() {
               @Override
               public void mouseClicked(MouseEvent e) {
                   deleteMouseClicked(e);
           p.add(delete);
           delete.setBounds(new Rectangle(new Point(430, 485), delete.getPreferredSize()));
           //---- okButton ----
           okButton.setText("OK");
           okButton.addMouseListener(new MouseAdapter() {
               @Override
               public void mouseClicked(MouseEvent e) {
                   okButtonMouseClicked(e);
           p.add(okButton);
           okButton.setBounds(335, 520, 75, okButton.getPreferredSize().height);
           //---- cancelButton ----
           cancelButton.setText("Cancel");
           cancelButton.addMouseListener(new MouseAdapter() {
               @Override
               public void mouseClicked(MouseEvent e) {
                   cancelButtonMouseClicked(e);
           p.add(cancelButton);
           cancelButton.setBounds(420, 520, 75, cancelButton.getPreferredSize().height);
           ss = ("test1,test2,test3,test4,test5"); //My string ss
           int length = ss.length();
           int asd = (ss.indexOf('_'))+1;
           real = ss.substring(asd, length);
           tokenizer = new java.util.StringTokenizer(real,",");
           tokenNo = tokenizer.countTokens();
           data = new ArrayList();
           values = new String [tokenNo];
//           Object[] arrayObject = data.toArray();// this is my initial code where arraylist is pass to object
               for(int i =0; i< tokenNo; i++)   // pass string-ss into arraylist individually
                data.add((tokenizer.nextToken(",")));
                //values[i] = tokenizer.nextToken(",");
                data.trimToSize();
                //System.out.println("tokenizer"  + values);
int aaaa = data.size();
System.out.println("size " + aaaa);
System.out.println("tokenizer" + tokenNo);
System.out.println("arraylist "+ i + data.get(i));
//JLIST
//======== scrollPane1 ========
//---- ManualList ---- This is my Jlist // copy arraylist into Object[] then pass it into JList
listModel = new DefaultListModel();
/* listModel = new DefaultListModel(); Part A also continue from above
* for (int i = 0; i< arrayObject.length;i ++)
* listModel.addElement(objectArray[i].toString());
* JList ManualList = new JList(listModel); //tried using listModel.method() to remove item in Jlist but return nullException
arrayObject = data.toArray();
JList ManualList=new JList(arrayObject);
ManualList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
ManualList.setSelectedIndex(0);
ManualList.setVisibleRowCount(5);
ManualList.setFont(new Font("Times New Roman", Font.PLAIN,12));
ManualList.setBorder(new MatteBorder(1, 1, 1, 1,Color.black));
ManualList.setLayoutOrientation(JList.VERTICAL_WRAP);
values = new String[tokenNo];
ManualList.addListSelectionListener(new ValueReporter());
// JScrollPane listPanel = new JScrollPane(ManualList);
scrollPane1.setViewportView(ManualList);
p.add(scrollPane1);
scrollPane1.setBounds(210, 435, 130, 75);
setVisible(true);
{ // compute preferred size
Dimension preferredSize = new Dimension();
for(int i = 0; i < p.getComponentCount(); i++) {
Rectangle bounds = p.getComponent(i).getBounds();
preferredSize.width = Math.max(bounds.x + bounds.width,preferredSize.width);
preferredSize.height = Math.max(bounds.y +bounds.height, preferredSize.height);
Insets insets = p.getInsets();
preferredSize.width += insets.right;
preferredSize.height += insets.bottom;
p.setMinimumSize(preferredSize);
p.setPreferredSize(preferredSize);
private void addMouseClicked(MouseEvent e)
private void deleteMouseClicked(MouseEvent e) //nthing happen here
int n =ManualList.getSelectedIndex();
if (!(n < 0) || (n > listModel.size()))
listModel.removeElement(arrayObject[n]);
delete.setEnabled(false);
ManualList.repaint();
ManualList.revalidate();
/* int n =ManualList.getSelectedIndex(); //tried using this but failed
if (!(n < 0) || (n > listModel.size()))
listModel.remove(n);
delete.setEnabled(false);
ManualList.repaint();
ManualList.revalidate();
private void okButtonMouseClicked(MouseEvent e) {
private void cancelButtonMouseClicked(MouseEvent e) {
private class ValueReporter implements ListSelectionListener {
public void valueChanged(ListSelectionEvent event) {
// if (!event.getValueIsAdjusting())
// gettext.setText(ManualList.getSelectedValue().toString());
//String name=(String) ManualList.getSelectedValue();
//System.out.println(name);
private void ManualListMouseClicked(MouseEvent e) {
// int n = (int)ManualList.getSelectedIndex();
// if (!(n < 0) || (n > listModel.size()))
// delete.setEnabled(true);
ok this is a small complete program
Thanks for the time to read this