FileName to write to a .txt File

[pramod reddy]

hai,
i am new to java.
i am developing an application, where the user enters a file or directory name and if it is a file ,then i have to write the filename to the .txt file.
i am using recusive method to test whther it is a file or directory, and if it is a file i want to write the name of the file to the .txt file, while running the below code i am getting the null pointer exception..
i think my declaration of BufferedWriter is wrong...
any suggestions are welcome.

and my code is here...

    import java.awt.event.*;
    import java.awt.*;
    import javax.swing.*;

    import java.io.*;
    import java.util.Calendar;
    import java.util.Date;




public class OldFileDeletions
{
// instance variables declaration //
	  private  static long size;
          private  static JTextArea jta ;
          private  static final String newline = "\n";
          File file;
          BufferedWriter bw;
 
    public static void main(String[] args) 
     {
	 
	  OldFileDeletions old = new OldFileDeletions();
     }

 
 

 OldFileDeletions()
      {
      JFrame frame = new JFrame("DISPLAYFILES");
      Container cp = frame.getContentPane();
      cp.setLayout(new FlowLayout());
      final JTextField text = new JTextField("",10); 
      cp.add(text);
   

      jta = new JTextArea(160,120);
      final JButton b = new JButton("Submit");
      cp.add(b);
      JScrollPane pane = new JScrollPane(jta); 
      pane.setVerticalScrollBarPolicy(
      JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

      cp.add(pane);
   //  frame.add(jta);
     

         b.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
          String s = text.getText();
          File file = new File(s) ;
       
        
          visitAllFiles(file);
       
             }
      });

      frame.setSize(300,250);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
 
   /* here is where real application works 
    * cheking for file or directory*/
 

          public  void visitAllFiles(File dir)
        
              { 
        	     
                 	if (dir.isDirectory()) 
                {

                     String[] files = dir.list();
                       for (int i=0; i<files.length; i++) 
                   {
   	                   visitAllFiles(new File(dir, files[i])); 
   	               }
               } 
                 	
                 	
                       else if(dir.isFile())
                       { 
                    
                         modify( dir);
                       }
                     
   	
           } 

/*   Retrieving file name based on last modified date and size*/
   
            public  void  modify(File dir)
         {
	 
	          
                  long length = dir.length();
                  size = length/1024;	
                  long lastmodified = dir.lastModified();
                  Date date =new Date (lastmodified);
                  Calendar cal = Calendar.getInstance();
                  Date date1 =cal.getTime();
                    // System.out.println(date1);
                   cal.add(Calendar.DATE, -14);

                   Date date2 =cal.getTime();
                   // System.out.println(date2);
                   long twoweekdate = dir.lastModified();
                   Date date3 =new Date (twoweekdate);

   
    	  try
 
    	  {
                       
    		         file = new File("C:\\Users\\promod\\Desktop\\read.txt");
                       
                        bw = new BufferedWriter(new FileWriter(file));
                       
                        
 
                      if((size>150) && (date3.after(date2)) )
      
                        {
	                   
	             
    	            
    	          
	                 
    	            	String filename = dir.getName();
	                 
    	                bw.write(filename+"\n" );
    	             
    	              
    	              
    	                }
    	  
                      else  if ( (size<150) && (date3.before(date2)) )
                       {
                    	 
  	                  
  	                        
                    	  
  	                   
                    		   
  	                	   bw.write("no files to display\n");
                    		
  	         
              
                       }
                      
        
    	  }
               catch(Exception ex)
            {
    	         ex.printStackTrace();
             }
              
        }
             
   
   }

[Ulf Dittmer]

Which line causes the exception? Which object is null?

[Carey Brown]

Line 77 will potentially set 'files' to null.

[Tim McGuire]

BufferedWriter will never print anything to the file until you call flush() on it.

you may want to handle cases in the modify method where your file doesn't match either of those if statements

[pramod reddy]

Thanks for your valuable suggestions......
i will go through it......