Solved

java.lang.NullPointerException?

Posted on 2002-04-09
5
218 Views
Last Modified: 2010-03-31
Please explain this error for me?
My code:
...
try {
     if(mySocket!=null){
          remoteIn = mySocket.getInputStream();
     }
} catch (Exception e) {
     System.out.println("Here's error: "+e.toString());
}

Print out: Here's error: java.lang.NullPointerException

What makes that error?
Thanks in advance.
GN

0
Comment
Question by:tgiangn
5 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 6928280
As has been said already, call e.printStackTrace()instead and post the error output.
0
 
LVL 3

Expert Comment

by:saxaboo
ID: 6928286
In a single-threaded environment, your test makes sure that mySocket is not null before invoking getInputStream, so the error means that getInpuStream itself throws an exception ...

In a multithreaded environment, your test doesn't seem safe (at least you did not provide enough code). Indeed, if mySocket is used by mutiple threads, it could be nulled out by another thread between your if() statement and your call to getInputStream.

=> 2 questions
1. are you multithreaded or not ?
2. could you post more code, such as socket opening ?

-S
0
 
LVL 1

Expert Comment

by:Moondancer
ID: 6956668
ADMINISTRATION WILL BE CONTACTING YOU SHORTLY.  Moderators Computer101 or Netminder will return to finalize these if still open in seven days.  Please post closing recommendations before that time.

Question(s) below appears to have been abandoned. Your options are:
 
1. Accept a Comment As Answer (use the button next to the Expert's name).
2. Close the question if the information was not useful to you, but may help others. You must tell the participants why you wish to do this, and allow for Expert response.  This choice will include a refund to you, and will move this question to our PAQ (Previously Asked Question) database.  If you found information outside this question thread, please add it.
3. Ask Community Support to help split points between participating experts, or just comment here with details and we'll respond with the process.
4. Delete the question (if it has no potential value for others).
   --> Post comments for expert of your intention to delete and why
   --> YOU CANNOT DELETE A QUESTION with comments; special handling by a Moderator is required.

For special handling needs, please post a zero point question in the link below and include the URL (question QID/link) that it regards with details.
http://www.experts-exchange.com/jsp/qList.jsp?ta=commspt
 
Please click this link for Help Desk, Guidelines/Member Agreement and the Question/Answer process.  http://www.experts-exchange.com/jsp/cmtyHelpDesk.jsp

Click you Member Profile to view your question history and please keep them updated. If you are a KnowledgePro user, use the Power Search option to find them.  

Questions which are LOCKED with a Proposed Answer but do not help you, should be rejected with comments added.  When you grade the question less than an A, please comment as to why.  This helps all involved, as well as others who may access this item in the future.  PLEASE DO NOT AWARD POINTS TO ME.

To view your open questions, please click the following link(s) and keep them all current with updates.
http://www.experts-exchange.com/questions/Q.11531498.html
http://www.experts-exchange.com/questions/Q.20178680.html
http://www.experts-exchange.com/questions/Q.20197366.html
http://www.experts-exchange.com/questions/Q.20270620.html
http://www.experts-exchange.com/questions/Q.20286506.html
http://www.experts-exchange.com/questions/Q.20286514.html
http://www.experts-exchange.com/questions/Q.20286565.html




*****  E X P E R T S    P L E A S E  ******  Leave your closing recommendations if this item remains inactive another seven (7) days.  If you are interested in the cleanup effort, please click this link http://www.experts-exchange.com/jsp/qManageQuestion.jsp?ta=commspt&qid=20274643 
POINTS FOR EXPERTS awaiting comments are listed here -> http://www.experts-exchange.com/commspt/Q.20277028.html
 
Moderators will finalize this question if in @7 days Asker has not responded.  This will be moved to the PAQ (Previously Asked Questions) at zero points, deleted or awarded.
 
Thank you everyone.
 
Moondancer
Moderator @ Experts Exchange
0
 
LVL 9

Expert Comment

by:Venci75
ID: 7940447
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:
PAQ'd and pts removed
Please leave any comments here within the next seven days.
 
PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
 
Venci75
EE Cleanup Volunteer
0
 

Accepted Solution

by:
modulo earned 0 total points
ID: 7990670
Finalized as proposed

modulo

Community Support Moderator
Experts Exchange
0

Featured Post

3 Use Cases for Connected Systems

Our Dev teams are like yours. They’re continually cranking out code for new features/bugs fixes, testing, deploying, testing some more, responding to production monitoring events and more. It’s complex. So, we thought you’d like to see what’s working for us.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

INTRODUCTION Working with files is a moderately common task in Java.  For most projects hard coding the file names, using parameters in configuration files, or using command-line arguments is sufficient.   However, when your application has vi…
Are you developing a Java application and want to create Excel Spreadsheets? You have come to the right place, this article will describe how you can create Excel Spreadsheets from a Java Application. For the purposes of this article, I will be u…
Viewers learn how to read error messages and identify possible mistakes that could cause hours of frustration. Coding is as much about debugging your code as it is about writing it. Define Error Message: Line Numbers: Type of Error: Break Down…
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question