y am i getting null pointer exception here?

this is the code and i am null pointer exception
class Server { String temp1,temp2,temp3,temp4; Vector confser=new Vector(1,1); ServerSocket ss; Socket s; confserver obj[]; int i=10; public Server() { try { ss = new ServerSocket(9999); while(true) { System.out.println("Waiting for you"); s= ss.accept(); System.out.println("done"); InputStream uis=s.getInputStream(); DataInputStream udis= new DataInputStream(uis); OutputStream uos=s.getOutputStream(); DataOutputStream udos=new DataOutputStream(uos); String Username=udis.readUTF(); String Usermode=udis.readUTF(); String Password=udis.readUTF(); String result=login(Username,Usermode,Password); udos.writeUTF(result); if(result=="LOGIN SUCCESS") { udos.writeUTF(Integer.toString(i)); System.out.println("thread" +i); obj[i]=new confserver(Username,Usermode,i); if (i == 10 ) obj[i].m=new messageQ(); obj[i].g.start(); obj[i].s.start(); i++; // confserver oocs[i]= new confserver(Username,Usermode); } ss.close(); uis.close(); uos.close(); System.out.println("connection terminated"); } } catch(Exception e) { System.out.println("the server Exception is "+e); } } public String login(String username,String usermode,String password) { String disp = "error"; try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection conn=DriverManager.getConnection("jdbc :-o dbc:gogoo"); PreparedStatement stmt=conn.prepareStatement("select * from login where username = ? "); stmt.setString(1,username); ResultSet result = stmt.executeQuery(); if(!result.next()) { System.out.println(usermode); if(usermode.equals("g")) { disp = "LOGIN SUCCESS"; Statement st=conn.createStatement(); st.executeUpdate("Insert into login values('" +username +"',' ','online')"); st.close(); System.out.println("Login Succes"); } else { disp = "Invalid UserName"; System.out.println("Login UnSuccesful"); } } else { temp1 = result.getString("username"); temp2 = result.getString("password"); temp3 = username; temp4 = password; if( temp2.equals(temp4)) { disp = "LOGIN SUCCESS"; System.out.println("Login Succes"); } else { disp = "LOGIN FAILED-Invalid Password"; System.out.println("Login UnSuccesful"); } } } catch(Exception excp) {} //conn.close(); return disp; } public static void main(String args[]) { Server objser=new Server(); } }

[ EFH: Fix code tags ]
Wat can b various reasons for getting null pointer exceptions
[ October 30, 2006: Message edited by: Ernest Friedman-Hill ]

NullPointerException always means that you've tried to access an object that simply isn't there; i.e., a variable's value is null instead of referring to an object. In general, it's a variable followed by a dot (or an open square bracket, if it's an array.)

This is far too much code for me to look at, but if you look at your stack trace it will tell you what line number the exception occurs on. If you then indicate to us exactly which line of code that is, I'm sure we can help you out.

You also need to use code tags. If you look at your code after you post, and your code is a mess, then you need to do something about it if you want people to answer your question.

Originally posted by sven studde:
You also need to use code tags.

To be fair: he did, they were just broken. I fixed them.

Do you use an IDE? If so, just check at which line the NullPointerException occurs.

[code]
confserver obj[];
//i am getting null pointer error in the following line wats the problem
obj[i].m=new messageQ();
obj[i].g.start();
obj[i].s.start();
[code]

confserver is class in defined how to create array of the class ?

Hi ranchers,

if the code compiles, the confserver object array must be non local.
Most probably the array is empty. If it is non local (i.e. an instance variable) it even may be not initialized.
In both cases (empty or uninitialized) a null pointer exception is thrown.


Simple example
class Main { Object [] o = new Object[5]; public static void main(String[] args) { new Main().foo(); } void foo(){ System.out.println(o[4]); System.out.println(o[4].toString()); } }

Prints null
and then throws NullPointerException.


By the way, Krishna, you should give classes identifiers that start with an uppercase letter. Makes the code easier to read (for humans, not for compilers).

krishna balaji wrote

confserver is class in defined how to create array of the class ?

confserver obj[];
It is declared but not defined and filled yet, not even an empty array, but a reference to a confserver array.
Please put the brackets behind the class identifier
confserver[] obj;
would be the normal way to say this. The way you did it works, but is unusual and also harder to read.
obj is not a nice name for a variable. It tells you nothing.

Declare, initialize and fill an array, example:
class Confserver { // mock class String message; } class Main { // instance variable [B]Confserver[] confi; // array declaration[/B] public static void main(String[] args) { Main main = new Main(); main.initConf(); main.output(main.confi); } private void initConf() { // array initialisation [B]confi = new Confserver[7];[/B] // fill array for (int index = 0; index < confi.length; index++) { // making the actual objects [B]confi[index] = new Confserver();[/B] // some mock messages confi[index].message = "confi #" + index; } } //only for output void output(Confserver[] confArray) { if (confArray != null) { for (int index = 0; index < confArray.length; index++) { System.out.print("conf["); System.out.print(index); System.out.print("] "); System.out.print("message:"); System.out.println(confArray[index].message); } } else { System.out.println("is null, not initialized"); } } }



Yours,
Bu.

Thank you sir that was very informative now i understand the problmem