import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        Socket clientSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        serverSocket = new ServerSocket(6000);

try {
            clientSocket = serverSocket.accept();
            System.out.println("Client connect");
            out = new PrintWriter(clientSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
while (true) {
                String inputLine = null;
                inputLine = in.readLine();
                System.out.println("클라이언트로부터 받은 문자열 : " + inputLine);
                out.println(inputLine);
if (inputLine.equals("quit"))
break;
            }
            out.close();
            in.close();
            clientSocket.close();
            serverSocket.close();
        } catch (Exception e){
            e.printStackTrace();
        }
    }

}

클라이언트

import android.app.Activity;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class MainActivity extends Activity {
private Socket socket;
    BufferedReader socket_in;
    PrintWriter socket_out;
    EditText input;
    Button button;
    TextView output;
    String data;

@Override
    public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
input = (EditText) findViewById(R.id.input);
button = (Button) findViewById(R.id.button);
output = (TextView) findViewById(R.id.output);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
                String data = input.getText().toString();
                Log.w("NETWORK", " " + data);
if(data != null) {
socket_out.println(data);
                }
            }
        });

        Thread worker = new Thread() {
public void run() {
try {
socket = new Socket("ip.ip.ip.ip", 6000);
socket_out = new PrintWriter(socket.getOutputStream(), true);
socket_in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                } catch (IOException e) {
                    e.printStackTrace();
                }
try {
while (true) {
data = socket_in.readLine();
output.post(new Runnable() {
public void run() {
output.setText(data);
                            }
                        });
                    }
                } catch (Exception e) {
                }
            }
        };
        worker.start();
    }

@Override
    protected void onStop() {
// TODO Auto-generated method stub
        super.onStop();
try {
socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

안드로이드 소켓통신의 간단한 예제입니다만 연결이 되지 않네요

socket = new Socket("ip.ip.ip.ip", 6000);

하면 연결이 되어야 하는데 연결이 되지않아서 그 다음부분인 

socket_out = new PrintWriter(socket.getOutputStream(), true);

이 되질않아서 

if(data != null) {
socket_out.println(data);
}

에서 에러가 뜨는걸로 생각됩니다...

로그캣의 MainActivity.java:42 부분이 여깁니다. 

socket_out.println(data);