Stop and Wait Protocol

Sender.java

import java.io.*;
import java.net.*;
public class Sender{
	Socket sender;
	ObjectOutputStream out;
	ObjectInputStream in;
	String packet,ack,str, msg;
	int n,i=0,sequence=0;
	Sender(){}
	public void run(){
		try{
			BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
			System.out.println("Waiting for Connection....");
			sender = new Socket("localhost",2005);
			sequence=0;
			out=new ObjectOutputStream(sender.getOutputStream());
			out.flush();
			in=new ObjectInputStream(sender.getInputStream());
			str=(String)in.readObject();
			System.out.println("reciver     > "+str);
			System.out.println("Enter the data to send....");
			packet=br.readLine();
			n=packet.length();
			do{
				try{

					if(i<n){
						msg=String.valueOf(sequence);
						msg=msg.concat(packet.substring(i,i+1));
					}else if(i==n){
						 msg="end";out.writeObject(msg);break;
					}out.writeObject(msg);
					sequence=(sequence==0)?1:0;
					out.flush();
					System.out.println("data sent>"+msg);
					ack=(String)in.readObject();
					System.out.println("waiting for ack.....\n\n");
					if(ack.equals(String.valueOf(sequence))){
						i++;
						System.out.println("receiver   >  "+" packet recieved\n\n");
					}else{    
						System.out.println("Time out resending data....\n\n");
						sequence=(sequence==0)?1:0;
					}}catch(Exception e){}
			}while(i<n+1);
			System.out.println("All data sent. exiting.");
		}catch(Exception e){}
		finally{
			try{
				in.close();
				out.close();
				sender.close();
			}
			catch(Exception e){}
		}
  }
		public static void main(String args[]){
			Sender s=new Sender();
			s.run();
		}
}