NullPointer Exception in a java client?

Question

I am coding a simple client, but I always get a NullPointerException at:

            while ((input = in.readLine()) != null) {

Here is my code:

public class ClientTest {

public static String server = "127.0.0.1";
public static int sport = 11111;
public static int cport = 11111;
private static String clientname="";
public static ExecutorService pool = Executors.newCachedThreadPool();
public static BufferedReader in = null;
public static PrintWriter out = null;
public static Socket socket = null;

public ClientTest(){
    this.clientname="";
}


public static void main(String[] args) {

    try {
        socket = new Socket(server, sport);
        out = new PrintWriter(socket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    } catch(IOException e) {
        System.out.println("could not create connection:\n" + e);
        try {
            if(socket != null) socket.close();
        } catch(Exception ex) {
            ex.printStackTrace();
        }
    }
    pool.execute(new Communicator());

}

public static class Communicator implements Runnable {
    @Override
    public void run() {
        String input = "";
        try {
            while ((input = in.readLine()) != null) {//here  i get the NPException
                StringTokenizer tokenizer = new StringTokenizer(input);
                tokenizer.nextToken();

                if(input.startsWith("!open")) {
                    if(tokenizer.hasMoreTokens()) System.out.print(tokenizer.nextToken() + "> ");
                    else System.out.print("> ");
                } 
                else if(input.startsWith("!exit")) {
                    System.out.print("Hallo hallo");
                } 
            }
        } catch(IOException e) {
            System.out.println("An error as occurred while reading from server - \n" + e);
        }
    }

}


}

Why do I get the NullPointerException? I am still initializing the String input.

you should add where you are getting null pointer exception or total error message — taufique
– taufique, Commented Oct 16, 2012 at 20:31
check what the value of in is ... chances are it is what's giving you the nullpointer exception. — Nabou
– Nabou, Commented Oct 16, 2012 at 20:31
Do you get a message says ' could not create connection: ...' If yes, socket itself not connected. — Satheesh Cheveri
– Satheesh Cheveri, Commented Oct 17, 2012 at 11:44

Jon Skeet · Accepted Answer · 2012-10-16 20:31:47Z

7

My question is, why do I get the NP Exception, I am still initializing the String input!

You would get a NullPointerException there if in is null... which it certainly could be. After all, if anything in the first part of main throws an exception, you catch it, print it out... and then keep going! So if socket.getOutputStream() throws an exception, both in and out will be null.

Moral: catching an exception and just continuing as if nothing had happened is very rarely a good idea.

answered Oct 16, 2012 at 20:31

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jon Skeet Over a year ago

@maximus: You only initialize it if an exception isn't thrown by earlier statements...

Tulains Córdova · Accepted Answer · 2012-10-16 20:36:46Z

0

I think something in the try block is failing and in is not being initialized, then after the exception you are running Comunicator and in is still null.

answered Oct 16, 2012 at 20:36

Tulains Córdova

2,6392 gold badges23 silver badges35 bronze badges

Collectives™ on Stack Overflow

NullPointer Exception in a java client?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related