I have to search a string in a file and write the matched lines to another file. I have a thread to read a file and a thread to write a file. I want to send the stringBuffer from read thread to write thread. Please help me to pass this. I amm getting null value passed.

write thread:

class OutputThread extends Thread{

/****************** Writes the line with search string to the output file *************/
    Thread runner1,runner;
    File Out_File;

    public OutputThread() {
    }
    public OutputThread(Thread runner,File Out_File) {
        runner1 = new Thread(this,"writeThread"); // (1) Create a new thread.
        this.Out_File=Out_File;
        this.runner=runner;
        runner1.start(); // (2) Start the thread.
    }


    public void  run()
    {

         try{
        BufferedWriter bufferedWriter=new BufferedWriter(new FileWriter(Out_File,true));
       System.out.println("inside write");
        synchronized(runner){
            System.out.println("inside wait");
            runner.wait();
        }
        System.out.println("outside wait");
        // bufferedWriter.write(line.toString());
        Buffer Buf = new Buffer();
        bufferedWriter.write(Buf.buffers);
        System.out.println(Buf.buffers);
        bufferedWriter.flush();

         }
         catch(Exception e){
         System.out.println(e);
         e.printStackTrace();
         }

    }

}

Read Thraed:

class FileThread extends Thread{

 Thread runner;
 File dir;
 String search_string,stats;
 File Out_File,final_output;
 StringBuffer sb = new StringBuffer();

    public FileThread() {
    }
    public FileThread(CountDownLatch latch,String threadName,File dir,String search_string,File Out_File,File final_output,String stats) {
        runner = new Thread(this, threadName); // (1) Create a new thread.
        this.dir=dir;
        this.search_string=search_string;
        this.Out_File=Out_File;
        this.stats=stats;
        this.final_output=final_output;
        this.latch=latch;
        runner.start(); // (2) Start the thread.
    }

  public void run()
  {

    try{
    Enumeration entries;
    ZipFile zipFile;
    String source_file_name = dir.toString();
    File Source_file = dir;
    String extension;
    OutputThread out = new OutputThread(runner,Out_File);

    int dotPos = source_file_name.lastIndexOf(".");
    extension = source_file_name.substring(dotPos+1);

    if(extension.equals("zip"))
    {
      zipFile = new ZipFile(source_file_name);
      entries = zipFile.entries();
      while(entries.hasMoreElements()) {
         ZipEntry entry = (ZipEntry)entries.nextElement();
         if(entry.isDirectory()) {
             (new File(entry.getName())).mkdir();
             continue;
            }
          searchString(runner,entry.getName(),new BufferedInputStream(zipFile.getInputStream(entry)),Out_File,final_output,search_string,stats);

      }

      zipFile.close();
     }

     else
      {

        searchString(runner,Source_file.toString(),new BufferedInputStream(new FileInputStream(Source_file)),Out_File,final_output,search_string,stats);

      }

    }

   catch(Exception e){
   System.out.println(e);
   e.printStackTrace();
  }

  }

  /********* Reads the Input Files and Searches for the String ******************************/

  public void searchString(Thread runner,String Source_File,BufferedInputStream in,File output_file,File final_output,String search,String stats)
  {
    int count = 0;   
    int countw = 0; 
    int countl=0;
    String s;
    String[] str;
    String newLine = System.getProperty("line.separator");

    try
    {

        BufferedReader br2 = new BufferedReader(new InputStreamReader(in));
        //OutputFile outfile = new OutputFile();  
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(output_file,true));
        Buffer Buf = new Buffer();
        //StringBuffer sb = new StringBuffer();
        StringBuffer sb1 = new StringBuffer();

              while((s = br2.readLine()) != null )
             {
                str = s.split(search);
                count = str.length-1;
                countw += count;
                if(s.contains(search)){
                   countl++;
                   sb.append(s);
                   sb.append(newLine);
                }
                if(countl%100==0)
                { System.out.println("inside count");
                    Buf.setBuffers(sb.toString());
                    sb.delete(0,sb.length());
                    System.out.println("outside notify");
                    synchronized(runner) 
                    { 
                       runner.notify(); 
                    } 

                    //outfile.WriteFile(sb,bufferedWriter);   
                    //sb.delete(0,sb.length());
                }
             }
        }


                    synchronized(runner) 
        { 
           runner.notify(); 
        } 

        br2.close();
        in.close();

        if(countw == 0)
        {
            System.out.println("Input File : "+Source_File );
            System.out.println("Word not found");
            System.exit(0);
        } 
        else
        {
            System.out.println("Input File : "+Source_File );
            System.out.println("Matched word count : "+countw );
            System.out.println("Lines with Search String : "+countl);
            System.out.println("Output File : "+output_file.toString());
            System.out.println();
                    } 
    }
    catch(Exception e){
        System.out.println(e);
        e.printStackTrace();
    }
 } 

}