Exception in thread "main" java.lang.NullPointerException at client.Server.main(Server.java:18)

Question

package client; import java.io.*; import java.net.*; import java.util.*; import java.awt.*; import javax.swing.*; public class Server { @SuppressWarnings("resource") public static void main(String[] args) { ServerSocket server =null; ServerThread thread; Socket you= null; while (true) { try{server = new ServerSocket(4331);} catch (IOException e1){System.out.println("正在监听");} try{you=server.accept(); System.out.println("客户的地址："+you.getInetAddress());} catch(IOException e){System.out.println("正在等待客户");} if(you!=null){ new ServerThread(you).start(); } } } } class ServerThread extends Thread { Socket socket; ObjectInputStream in=null; ObjectOutputStream out =null; JFrame window; JTextArea text; ServerThread(Socket t) { socket =t; try { out=new ObjectOutputStream(socket.getOutputStream()); in =new ObjectInputStream(socket.getInputStream()); } catch (IOException e){}         window =new JFrame();         text =new JTextArea();         for(int i=1;i<=20;i++)         {          text.append("你好，我是服务器上的文件区组件\n");         }         text.setBackground(Color.yellow);         window.add(text);         window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } public void run(){ try{  out.writeObject(window);} catch (IOException e){ System.out.println("客户离开"); } } } 附客服代码 package client; import java.io.*; import java.net.*; import java.util.*; public class Client { public static void main(String agrs[]) { Scanner scanner= new Scanner (System.in); Socket mysocket=null; ObjectInputStream inObject=null; ObjectOutputStream outObject=null; Thread thread; ReadWindow readWindow =null; try { mysocket =new Socket(); readWindow =new ReadWindow(); thread =new Thread(readWindow); System.out.println("输入服务器的IP"); String IP=scanner.nextLine(); System.out.println("输入端口号："); int port =scanner.nextInt(); if(mysocket.isConnected()) { } else  { InetAddress address =InetAddress.getByName(IP); InetSocketAddress socketAddress=new InetSocketAddress(address,port); mysocket.connect(socketAddress); InputStream in=mysocket.getInputStream();     OutputStream out=mysocket.getOutputStream();     inObject=new ObjectInputStream(in);     outObject=new ObjectOutputStream(out);     readWindow.setObjectInputStream(inObject);     thread.start(); } } catch(Exception e) { System.out.println("服务器已经断开"+e); } } } class ReadWindow implements Runnable {     ObjectInputStream in;     public void setObjectInputStream( ObjectInputStream in)     {      this .in=in;     }     public void run()     {      double result =0;      while (true)      {      try{      javax.swing.JFrame window=(javax.swing.JFrame)in.readObject();      window.setTitle("这是从服务器上读入的窗口");      window.setVisible(true);      window.requestFocusInWindow();      window.setSize(600, 800);      }      catch (Exception e)      {      System.out.println("服务器已经断开"+e);      break;      }      }     } }