Probleme socket

Bonjour,
j ai un tp qui propose de faire un programme serveur qui compte les caracteres recus et renvoie le total courant au programme client a travers outputstream de sa socket z chaque fois qu un caratere est recu
mon code
server.java

package tt;

import java.io.*;
import java.net.*;


public class server {
public static void main(String args[]) throws IOException{
ServerSocket s=new ServerSocket(20000);
System.out.println("serveur en ecoute sur le port "+
s.getLocalPort());
Socket conn= s.accept();
System.out.println("connexion reçue depuis"+
		conn.getRemoteSocketAddress());
PrintStream out = new PrintStream(conn.getOutputStream());
InputStream in=conn.getInputStream();
while(true)
{   String str = in.readLine();
    System.out.println(str); 
	}


		conn.close();
	System.out.println("fin du flux de donnees");	


}
}

client.java

package tt;

import java.io.*;
import java.net.*;

public class client {
	public static void main(String args[]) throws IOException{
Socket s=new Socket("localhost",20000);
PrintStream out= new PrintStream(s.getOutputStream());
InputStream in=s.getInputStream();
String str="Salut";
int len=str.length();
System.out.println(str+""+len);

str=in.readLine();   

s.close();
	}	
}

a l'execution de client j

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	The method readLine() is undefined for the type InputStream

	at tt.client.main(client.java:15)

et server

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	The method readLine() is undefined for the type InputStream

	at tt.server.main(server.java:18)

aider moi svp