NullPointerException

[nephilim89]

ciao!
errore:

Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1045)
at javax.swing.JToolBar.addImpl(JToolBar.java:561)
at java.awt.Container.add(Container.java:365)
at src.myApp.<init>(myApp.java:39)
at src.myApp.main(myApp.java:90)

codice:

 package src;
import java.awt.*;
import java.awt.event.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import java.sql.*;
import javax.swing.table.DefaultTableModel;
import javax.swing.JTable;
import java.util.Vector;

class myApp extends JFrame implements ActionListener{

private Button ok;
private Button annulla;
private JPanel northPanel;
private JTable mainTable;
private JPanel statusBar;
private JProgressBar progressBar;
private JMenuBar menuBar;
private JMenu fileMenu;
private JMenuItem nuovoFile;
private BorderLayout borderLayout;
private JToolBar toolBar;


public myApp(){
    
    borderLayout = new BorderLayout();
    this.setLayout(borderLayout);    
        
        northPanel = new JPanel(new GridLayout(2,1));

        menuBar = new JMenuBar();
            menuBar.add(fileMenu = new JMenu("File"));
                fileMenu.add(nuovoFile = new JMenuItem("Nuovo"));

        toolBar = new JToolBar("toolBar",JToolBar.HORIZONTAL);
            toolBar.add(ok);
            toolBar.add(annulla);

      ok = new Button("Ok");
    ok.addActionListener(this);
    
    annulla = new Button("Annulla");
    annulla.addActionListener(this);

        statusBar = new JPanel(new GridLayout(1,1));

        northPanel.add(menuBar);
        northPanel.add(toolBar);




        this.add(northPanel,BorderLayout.NORTH);
    this.add(mainTable,BorderLayout.CENTER);
    this.add(statusBar,BorderLayout.SOUTH);
    this.setTitle("mia finestra");
    this.setSize(900,600);
    this.setVisible(true);

    this.addWindowListener(new WindowAdapter(){
        public void windowClosing(WindowEvent e){
            dispose();
        }
        public void windowIconified(WindowEvent e){
            setTitle("Ridotto a Icona");
        }
        public void windowDeiconified(WindowEvent e){
            setTitle("mia finestra");
        }
        } ) ;
    
}



public void actionPerformed(ActionEvent e){

System.out.println(e);
}

public static void main(String arg[])
{

    myApp launch = new myApp();

}

} 

soluzione?