PipedInputStream / PipedOutputStream with two threads problem....pls help

Hi there,
  I want to communicate two threads using pipe. Also I want to make
this process as cyclic process, currently it is non-cyclic
I am posting my code below
pls suggest something...........

//Pipe Writer class

import java.io.*;
public class Pipe_Writer extends Thread {
    PipedWriter pWriter = new PipedWriter();
    public Pipe_Writer() {}

    public PipedWriter getPipedWriter() {
        return pWriter;
    }

    public void run() {
        Process p = null;
        try {
            p = Runtime.getRuntime().exec("cmd");
        } catch (IOException e) {
            e.printStackTrace();
        }
        BufferedReader reader = new BufferedReader(new
InputStreamReader(p.getInputStream()));
        BufferedWriter writer = new BufferedWriter(new
OutputStreamWriter(p.getOutputStream()));

        BufferedReader reader2 = new BufferedReader(new
InputStreamReader(System.in));

        String line;
        String rd = "";
        try {
            rd = reader2.readLine();
            System.out.println(rd);
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        try {
            // writer.write("dir\n"); //writing to process
            writer.write(rd + "\n");
            writer.flush();
            while ((line = reader.readLine()) != null) {
                    System.out.println(line);
                    pWriter.write(line); //writing to pipe
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

=========================================

// Pipe reader class

import java.io.*;
public class Pipe_Reader extends Thread{
    PipedReader pReader;

    public Pipe_Reader(Pipe_Writer writer)throws IOException{
        pReader = new PipedReader(writer.getPipedWriter());
    }

    public void run(){
        try {
            while(true){
                System.out.println((char)pReader.read()); //Reading from pipe
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

=============================

// main method

public static void main(String[] args)throws IOException {
        Pipe_Writer writer = new Pipe_Writer();
        Pipe_Reader reader = new Pipe_Reader(writer);
        writer.start();
        reader.start();
    }
====================================

pls HELP me!.....