java - trouble using printwriter from another class -

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my main problem nullpointerexception when use chatpanel.pw.println(chatpanel.name + " has disconnected chat.") while printwriter in chatpanel class , i'm trying use printwriter send message through socket. if me understand , maybe give me solution problem. did remove lot of code but, should compile.

import java.io.*; import java.awt.*; import java.net.*; import javax.swing.*; import java.awt.event.*; import javax.swing.jcomponent; public class chatframe1 extends jframe{      public chatframe1(){       setlayout(new gridbaglayout());       setsize(1000,600);         settitle("chat");       setresizable(true);         addwindowlistener(new windowadapter(){          public void windowclosing(windowevent we){              //the problem here.             chatpanel.pw.println(chatpanel.name + " has disconnected chat.");             system.out.println(chatpanel.name);             system.exit(0);         }       });       chatpanel sp = new chatpanel();       setvisible(true);    }    public static void main(string[] args){         new chatframe1();      } } class chatpanel extends jpanel implements actionlistener, runnable{     thread t;     jtextfield tf;     jtextarea ta;     jbutton b;     socket s;     bufferedreader br;     public static printwriter pw;     string temp;     boolean connected;     public static string name;      public chatpanel(){          gridbagconstraints gbc = new gridbagconstraints();         name = (string)joptionpane.showinputdialog(null,"enter username "+                 "(please use letters , numbers) :",                  "username login",                 joptionpane.plain_message, null, null, "user-name");         setlayout(new gridbaglayout());         tf = new jtextfield();         tf.addactionlistener(this);         ta = new jtextarea();         b = new jbutton("press connect");         b.addactionlistener(this);      }     public void actionperformed(actionevent ae){         if((tf != null) && (!connected)){          b.setlabel("press connect");         }         if((ae.getsource() == b) && (!connected)){             try{                 s = new socket("127.0.0.1", 2020);                 pw = new printwriter(s.getoutputstream(), true);                 tf.settext("");              }catch(unknownhostexception uhe){                 system.out.println(uhe.getmessage());               }catch(ioexception ioe){                  system.out.println(ioe.getmessage());              }                connected = true;             t = new thread(this);             b.setlabel("disconnect");             t.start();          }else if((ae.getsource() == b) && (connected)){               connected = false;             try{                 pw.println(name +" has disconnected chat.");                 ta.settext("");                 s.close(); //no buffering so, ok             }catch(ioexception ioe){                 system.out.println(ioe.getmessage());             }             b.setlabel("press reconnect");         }else{         temp = tf.gettext();             tf.settext("");         }     }     public void run(){          try{             bufferedreader br = new bufferedreader(new inputstreamreader(s.getinputstream()));             while(((temp = br.readline()) != null) && connected){             ta.append(temp + "\n");             }         }catch(ioexception ioe){             system.out.println(ioe.getmessage());         }     } }

i think giving nullpointerexception

chatpanel.pw.println(chatpanel.name + " has disconnected chat.");

because chatpanel.pw has never been initialized in code, , therefore null

you should ensure chatpanel.pw has been initialized somewhere (maybe within constructor) inside chatpanel class before calling chatpanel.pw.println()


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