sockets - Java.net server example doesn't work -

this question has answer here:

• example socket app doesn't work 1 answer

i'm new java.net , trying make simple client-server app. here server code:

public class consumer extends thread{      public socket s;     int num;      public consumer(int num, socket s){         this.num = num;         this.s = s;          setdaemon(true);         setpriority(norm_priority);         start();     }      public static void main(string args[]){         try {             int = 0;              serversocket server = new serversocket(3128, 0, inetaddress.getbyname("localhost"));              system.out.println("server started");             while (true){                 new consumer(i, server.accept());                 i++;             }         } catch (exception e){          }     }      public void run(){         try {             inputstream = s.getinputstream();             outputstream os = s.getoutputstream();              byte buf[] = new byte[64*1024];             int r = is.read(buf);              string data = new string(buf, 0, r);              data = "" +num+": " +"\n" + data;              os.write(data.getbytes());              s.close();         } catch (exception e){             system.out.println("init error: " + e);         }     }  } 

when start - nothing bad happens when send smth client following:

init error: java.lang.stringindexoutofboundsexception: string index out of range: -1 

how fix it?

when read data input stream, know you've reached end of stream when read returns -1. looks that's happens here: r comes out -1 because there's no data read, , program goes on try create string negative number of characters.

you should check return values of functions error conditions:

        int r = is.read(buf);          if (r < 0) return; /* end of stream reached */ 

also, when handling exceptions should print stack trace. stack trace tells on line of program exception happened. without information have start debugging process guessing.

    } catch (exception e){         system.out.println("init error: " + e);         e.printstacktrace();     }