Java: exception dans le fil "AWT-EventQueue-0" java.lang.NullPointerException

Question

public class MainFrame extends JFrame { 
    public DefaultTableModel historyModel; 
    public DefaultTableModel dataModel; 
    public JTable historyTable; 
    public JTable dataTable; 
    public JTableHeader header; 

private void createUI() { 
     browsersTabbedPane = new BrowsersTabbedPane(); 
     add(browsersTabbedPane.getTabPane(), CENTER); 
     addDefaultBrowserComponentForTabbedPane(); 
     createActions(); 
     add(createToolBar(), BorderLayout.NORTH); 
     add(createStatusBar(), BorderLayout.SOUTH); 
     add(createDataView(dataModel,dataTable, header), BorderLayout.PAGE_END); 
     add(createHistoryView(historyModel,historyTable), BorderLayout.LINE_END); 
     add(createBigButton(browsersTabbedPane.getActiveBrowser(),dataModel,historyModel,dataTable,historyTable), BorderLayout.WEST); 

     createMenuBar(); 
    } 

private JPanel createDataView(DefaultTableModel dataModel, JTable dataTable, JTableHeader header){ 
     JPanel panel = new JPanel(); 

     Object data[][] = {{"001","vinod","Bihar","India","Biology","65","First"}, 
          {"002","Raju","ABC","Kanada","Geography","58","second"}, 
          {"003","Aman","Delhi","India","computer","98","Dictontion"}, 
          {"004","Ranjan","Bangloor","India","chemestry","90","Dictontion"}, 
          {"004","Ranjan","Bangloor","India","chemestry","90","Dictontion"}}; 
     Object col[] = {"Roll","Name","State","country","Math","Marks","Grade"}; 
     dataModel = new DefaultTableModel(data,col); 
     dataTable = new JTable(dataModel); 

     dataTable.setPreferredScrollableViewportSize(new Dimension(1500,100)); 
     header = dataTable.getTableHeader(); 
     header.setBackground(Color.yellow); 
     JScrollPane pane = new JScrollPane(dataTable); 
     dataTable.setAutoResizeMode(JTable.WIDTH); 
     dataTable.doLayout(); 
     panel.add(pane); 
     return panel; 

    } 

    private JPanel createBigButton(Browser browser, DefaultTableModel dataModel, DefaultTableModel historyModel, JTable dataTable, JTable historyTable){ 
     JPanel panel = new JPanel(); 
     JButton bigbutton = new JButton("Big Button"); 
     bigbutton.addActionListener(new BigButtonListener(browser,dataModel,historyModel,dataTable, historyTable)); 
     panel.add(bigbutton); 
     return panel; 
    } 

    class BigButtonListener implements ActionListener{ 
     Image screenshot; 
     Browser bigbrowser; 

     BigButtonListener(Browser browser, DefaultTableModel dataModel, DefaultTableModel historyModel, JTable dataTable, JTable historyTable) { 
      screenshot = browser.toImage(true); 
      bigbrowser = browser; 
      historyModel = historyModel; 
      dataModel = dataModel; 
      dataTable = dataTable; 
      historyTable = historyTable; 
      //table1.addRow 
     } 

     @Override 
     public void actionPerformed(ActionEvent e) { 
      // save current image   
      //historyModel.insertRow(2,new Object[]{"Sushil"}); 
      System.out.println(historyTable.getRowCount()); 

     } 
    } 
} 

Le problème se produit lorsque le bouton Big est cliqué. Il est censé générer le nombre total de lignes de l'historiqueTable (qui est public).

mais c'est la sortie stacktrace

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at com.my.demo.MainFrame$BigButtonListener.actionPerformed(MainFrame.java:356) 
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) 
    at java.awt.Component.processMouseEvent(Unknown Source) 
    at javax.swing.JComponent.processMouseEvent(Unknown Source) 
    at java.awt.Component.processEvent(Unknown Source) 
    at java.awt.Container.processEvent(Unknown Source) 
    at java.awt.Component.dispatchEventImpl(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Window.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(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) 

Answer 1

Vous n'initialisez historyTable à une valeur non nulle.

Answer 2

Vous utilisez la historyTable de classe variable locale à se fixer, ce qui est à son tour la mise en elle-même nulle parce que la valeur initiale était nulle, ne permettant pas vos données souhaitées à récupérer