Re: please help to debug error

Lew <>
Sat, 25 Aug 2007 14:45:00 -0400
darker side wrote:

public class cli

Nearly universal convention in Java is to name classes with an initial
upper-case letter.

    public static void main(String args[]) throws IOException

        Socket cli=new Socket(InetAddress.getByName("localhost"),1233);
        System.out.println("connected by client");
         DataInputStream dis=new DataInputStream(;
         DataOutputStream dos=new
         String inp=dis.readLine();

Are you familiar with the API docs?
Did you notice the boldface warning?


Joshua Cranmer wrote:

What do you think this method is doing? Look at it carefully, since
there is something that most people would logically expect it to do but
it doesn't do...

Hint: dos.something()?

Joshua Cranmer wrote:

In addition, you should explicitly close the Socket when you are
finished using it.

darker side wrote:

Exception in thread "main" java.lang.NullPointerException
        at java.lang.String.<init>(

Joshua Cranmer wrote:

There is only one reason why the constructor of String would throw a
NullPointerException: the String being passed in is null. Now, ask
yourself why the input from the socket is null (hint: look at your
client class. What isn't it doing?).


Some other points-of-order:
@ Don't use tab's in Usenet posts. It screws up formatting.
@ Use proper English grammar, including capitalization and punctuation.
@ It generally helps to go through the Java APIs if you need help.

I was echoing Joshua's point, specifically about the readLine() method. The
general URL for the API docs is


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