title: Java Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException error
body: <p>I have tried to go over this my self but i do not know how to resolve this.</p>
  
  <p>I am getting this error when i try and run my addressBookUi class.</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
  at addressBookUI.startComponents(addressBookUI.java:43)
  at addressBookUI.&lt;init&gt;(addressBookUI.java:6)
  at addressBookUI$2.run(addressBookUI.java:143)
  at java.awt.event.InvocationEvent.dispatch(Unknown Source)
  at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
  at java.awt.EventQueue.access$000(Unknown Source)
  at java.awt.EventQueue$3.run(Unknown Source)
  at java.awt.EventQueue$3.run(Unknown Source)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
  at java.awt.EventQueue.dispatchEvent(Unknown Source)
  at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
  at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
  at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
  at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
  at java.awt.EventDispatchThread.run(Unknown Source)
  </code></pre>
  
  <p>Here is my addressBookUi class</p>
  
  <pre><code>    import javax.swing.table.DefaultTableModel;
  
  public class addressBookUI extends javax.swing.JFrame {
  
      public addressBookUI() {
          startComponents();
      }
  
      private void startComponents() {
          mainScrollPane = new javax.swing.JScrollPane();
          mainTable = new javax.swing.JTable();
          addButton = new javax.swing.JButton();
          saveButton = new javax.swing.JButton();
          deleteButton = new javax.swing.JButton();
          mainMenuBar = new javax.swing.JMenuBar();
          mainMenu = new javax.swing.JMenu();
          newMenuItem = new javax.swing.JMenuItem();
          openMenuItem = new javax.swing.JMenuItem();
          saveMenuItem = new javax.swing.JMenuItem();
          printMenuItem = new javax.swing.JMenuItem();
          quitMenuItem = new javax.swing.JMenuItem();
          editMenuBar = new javax.swing.JMenu();
          editPersonsMenuItem = new javax.swing.JMenuItem();
          sortNameMenuItem = new javax.swing.JMenuItem();
          sortPostcodeMenuItem = new javax.swing.JMenuItem();
  
          setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
  
          mainTable.setModel(new javax.swing.table.DefaultTableModel(
                  new Object[][] { { null, null, null, null },
                          { null, null, null, null }, { null, null, null, null },
                          { null, null, null, null } }, new String[] { "Title 1",
                          "Title 2", "Title 3", "Title 4" }));
  
          mainScrollPane.setViewportView(mainTable);
  
          addButton.setText("Add");
  
          saveButton.setText("Save Row");
  
          deleteButton.setText("Delete Row");
  
          refreshButton.setText("Refresh");
          refreshButton.addActionListener(new java.awt.event.ActionListener() {
              public void actionPerformed(java.awt.event.ActionEvent evt) {
                  refreshButtonActionPerformed(evt);
              }
          });
  
          mainMenu.setText("File");
  
          newMenuItem.setText("New");
          mainMenu.add(newMenuItem);
  
          openMenuItem.setText("Open");
  
          saveMenuItem.setText("Save");
          mainMenu.add(saveMenuItem);
  
          printMenuItem.setText("Print");
          mainMenu.add(printMenuItem);
  
          quitMenuItem.setText("Quit");
          mainMenu.add(quitMenuItem);
  
          mainMenuBar.add(mainMenu);
  
          editMenuBar.setText("Edit");
  
          editPersonsMenuItem.setText("Edit Selected Persons");
          editMenuBar.add(editPersonsMenuItem);
  
          sortNameMenuItem.setText("Sort by Name");
          editMenuBar.add(sortNameMenuItem);
  
          sortPostcodeMenuItem.setText("Sort by Postcode");
          editMenuBar.add(sortPostcodeMenuItem);
  
          mainMenuBar.add(editMenuBar);
  
  //      mainMenuBar.add(helpMenuBar);
  
          setJMenuBar(mainMenuBar);
  
          javax.swing.GroupLayout layout = new javax.swing.GroupLayout(
                  getContentPane());
          getContentPane().setLayout(layout);
          layout.setHorizontalGroup(layout
                  .createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                  .addComponent(mainScrollPane)
                  .addGroup(
                          layout.createSequentialGroup()
                                  .addContainerGap()
                                  .addComponent(addButton,
                                          javax.swing.GroupLayout.PREFERRED_SIZE,
                                          155,
                                          javax.swing.GroupLayout.PREFERRED_SIZE)
                                  .addGap(18, 18, 18)
                                  .addComponent(saveButton,
                                          javax.swing.GroupLayout.PREFERRED_SIZE,
                                          155,
                                          javax.swing.GroupLayout.PREFERRED_SIZE)
                                  .addGap(18, 18, 18)
                                  .addComponent(deleteButton,
                                          javax.swing.GroupLayout.PREFERRED_SIZE,
                                          155,
                                          javax.swing.GroupLayout.PREFERRED_SIZE)
                                  .addGap(18, 18, 18)
                                  .addComponent(refreshButton,
                                          javax.swing.GroupLayout.PREFERRED_SIZE,
                                          155,
                                          javax.swing.GroupLayout.PREFERRED_SIZE)
                                  .addContainerGap(51, Short.MAX_VALUE)));
          layout.setVerticalGroup(layout
                  .createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                  .addGroup(
                          layout.createSequentialGroup()
                                  .addComponent(mainScrollPane,
                                          javax.swing.GroupLayout.PREFERRED_SIZE,
                                          163,
                                          javax.swing.GroupLayout.PREFERRED_SIZE)
                                  .addPreferredGap(
                                          javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                                  .addGroup(
                                          layout.createParallelGroup(
                                                  javax.swing.GroupLayout.Alignment.BASELINE)
                                                  .addComponent(addButton)
                                                  .addComponent(saveButton)
                                                  .addComponent(deleteButton)
                                                  .addComponent(refreshButton))
                                  .addGap(0, 17, Short.MAX_VALUE)));
  
          pack();
      }
  
      private void refreshButtonActionPerformed(java.awt.event.ActionEvent evt) {// GEN-FIRST:event_refreshButtonActionPerformed
  
      }
  
      public static void main(String[] args) {
          java.awt.EventQueue.invokeLater(new Runnable() {
              public void run() {
                  new addressBookUI().setVisible(true);
              }
          });
  
      }
  
  //  protected javax.swing.JMenuItem aboutHelpMenuBar;
      protected javax.swing.JButton addButton;
      protected javax.swing.JButton deleteButton;
      private javax.swing.JMenu editMenuBar;
      protected javax.swing.JMenuItem editPersonsMenuItem;
      private javax.swing.JMenu mainMenu;
  //  private javax.swing.JMenu helpMenuBar;
      private javax.swing.JScrollPane mainScrollPane;
      private javax.swing.JMenuBar mainMenuBar;
      protected javax.swing.JTable mainTable;
      protected javax.swing.JMenuItem newMenuItem;
      protected javax.swing.JMenuItem openMenuItem;
      protected javax.swing.JMenuItem printMenuItem;
      protected javax.swing.JMenuItem quitMenuItem;
      protected javax.swing.JButton refreshButton;
      protected javax.swing.JButton saveButton;
      protected javax.swing.JMenuItem saveMenuItem;
      protected javax.swing.JMenuItem sortNameMenuItem;
      protected javax.swing.JMenuItem sortPostcodeMenuItem;
  }
  </code></pre>
  
  <p>If anyone could help that would be great</p>