• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Ron McLeod
  • Paul Clapham
  • Devaka Cooray
  • Tim Cooke
Sheriffs:
  • Rob Spoor
  • Liutauras Vilda
  • paul wheaton
Saloon Keepers:
  • Tim Holloway
  • Tim Moores
  • Mikalai Zaikin
  • Carey Brown
  • Piet Souris
Bartenders:
  • Stephan van Hulst

java.lang.NullPointerException at runtime

 
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
i get these errors when i'm trying to add data


My coding...
 
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
You didn't initialize your queArray instance variable -- in your Queue inner class... hence, it is null.

Henry
 
Author
Posts: 12617
IntelliJ IDE Ruby
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
More specifically, this is what's in your constructor:The stack trace gives the precise line in your code that starts down the path to the exception. One you have that line number, work backwards in your code.

The code is nearly unreadable because of the lack of proper indentation. Also, class names should begin with a capital letter.
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
@Henry Wong
i initialized queArray variable


this time i don't get any errors but it does not get filled up so when i retrieve it is EMPTY
 
David Newton
Author
Posts: 12617
IntelliJ IDE Ruby
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Please UseAMeaningfulSubjectLine when posting. Explaining your question or remark briefly on the subject line allows us to know what we are getting into, and if we will be able to help.
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
@Henry Wong Subject line is changed Thank for the info
 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:@Henry Wong
i initialized queArray variable


this time i don't get any errors but it does not get filled up so when i retrieve it is EMPTY




That's not the correct fix. The correct fix is to do it correctly in your constructor. With this change, the array size and the maxsize variable may be out of sync.

Henry
 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:@Henry Wong Subject line is changed Thank for the info



Thanks for letting me know... but it wasn't me who requested it...

Henry
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
This is functioning properly
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
this is the line throwing exception
 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:This is functioning properly



Depends on what you mean by functioning properly. If one of the tasks to do is to initialize the queArray *instance* variable, then your constructor doesn't do that.

Henry
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
When i'm debugging

above lines are successfully executed and the variable values are
queArray==#1020(length=5)
maxSize==5

 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:When i'm debugging

above lines are successfully executed and the variable values are
queArray==#1020(length=5)
maxSize==5




Yes... but what about the queArray *instance* variable? I believe you that you set the queArray *local* variable correctly.

Henry
 
David Newton
Author
Posts: 12617
IntelliJ IDE Ruby
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
IT'S LOCAL TO THE CONSTRUCTOR. Please KeepItDown, self.

It's local to the constructor.
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
queArray is not null
 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:queArray is not null



Sorry, I can't think of anymore hints to get you to the solution. Just change this (in the constructor) ...



to this...




Henry
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
i'm really sorry, it's just i'm a beginner but thank you very much for trying to help me out
i get no error but when i try to retrieve, it is empty
 
Henry Wong
author
Posts: 23956
142
jQuery Eclipse IDE Firefox Browser VI Editor C++ Chrome Java Linux Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:
i get no error but when i try to retrieve, it is empty



Not unexpected. All we did was help you fix one bug. You didn't expect to only have one bug right?

You still have to debug the application to locate the others.

Henry
 
Ranch Hand
Posts: 42
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Bhathiya Pathirana wrote:i'm really sorry, it's just i'm a beginner but thank you very much for trying to help me out
i get no error but when i try to retrieve, it is empty



Hi.
It's a similar error to your first one. You need to learn about the scope of instances of objects/variables.


Do you understand why that was wrong?


Can you see the conflict?

If I were you I would start with a simple example. You are using inheritance, a GUI, inner classes- all very advanced topics. Start off with a very simple example where you can enter your name and get it to return it back to you(System.out.print() will do fine!). After that get it to store a number of names and print them all back to you. Once you can do that you can start worrying about creating Person classes with name/email fields etc.

Good luck!
 
Sheriff
Posts: 22809
132
Eclipse IDE Spring Chrome Java Windows
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Eoin Brosnan wrote:Can you see the conflict?


You mean that compiler error on line 11? But if you leave out the "private" on that line then your example is a good one of local variables shadowing / hiding instance fields.
 
Eoin Brosnan
Ranch Hand
Posts: 42
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Rob Prime wrote:

Eoin Brosnan wrote:Can you see the conflict?


You mean that compiler error on line 11? But if you leave out the "private" on that line then your example is a good one of local variables shadowing / hiding instance fields.



Once I turned off my PC last night I felt that I had made that error! Updated.
 
Bhathiya Pathirana
Greenhorn
Posts: 9
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Thank you very much for you all guys being so supportive and kind about me, can anyone please let me have some hints for where i should start learning from? course names or training materials, so i can start having a good foundation..
 
Every time you till, you lose 30% of your organic matter. But this tiny ad is durable:
New web page for Paul's Rocket Mass Heaters movies
https://coderanch.com/t/785239/web-page-Paul-Rocket-Mass
reply
    Bookmark Topic Watch Topic
  • New Topic