nullpointer exception while using jfile chooser

Question

I am getting nullpointer exception by clicking on btn obt which is nullpointerexception thrown by jfilechooser. Don't know what to do for this problem "re=jf.showOpenDialog(null);" Can anyone please salve this error?

public void actionPerformed(ActionEvent e)
{
    if (e.getSource()==obt) 
    { 

        try
        {
        int re = jf.showOpenDialog(null);   
            if(re==JFileChooser.APPROVE_OPTION)
            {
                File f=jf.getSelectedFile();
                t1.append("Opening:"+f.getName()+ ".");
            }
            else
            {
                t1.append("Open command cancelled by user." );
            }

            t1.setCaretPosition(t1.getDocument().getLength());
        }
        catch(Exception ee)
        {
            System.out.println(ee);
        }
    }
    else if(e.getSource()==ebt)
    {
        try
        {
            int re=jf2.showSaveDialog(null);
            if(re==JFileChooser.APPROVE_OPTION)
            {
                File f=jf2.getSelectedFile();
                t1.append("Extracting:");//+f.getName()+ ".");
            }
            else
            {
                t1.append("Extract command cancelled by user.");
            }

            t1.setCaretPosition(t1.getDocument().getLength());
            }
        catch(Exception ee)
        {
            System.out.println(ee);
        }
    }
}