• 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
  • Jeanne Boyarsky
  • Ron McLeod
  • Paul Clapham
  • Liutauras Vilda
Sheriffs:
  • paul wheaton
  • Rob Spoor
  • Devaka Cooray
Saloon Keepers:
  • Stephan van Hulst
  • Tim Holloway
  • Carey Brown
  • Frits Walraven
  • Tim Moores
Bartenders:
  • Mikalai Zaikin

NullPointerException

 
Ranch Hand
Posts: 46
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
hi!
Could you please explain the java.lang.NullPointerException.
Thanks and Regards
Usman
 
Greenhorn
Posts: 28
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
A NullPointerException is thrown when you call a method / variable from a reference that doesn't point anywhere.
See the following example class. In the main() method, we create a reference and an object and then set it to null. The reference e doesn't point anywhere when the method show() is called. Thus, JVM generates a NullPointerException.

public class example {
public void show() {
}

public static void main (String args[]) {
example e = new example();
e = null;
e.show();
}
}
Muhammad Ali Shah
Karachi, Pakistan.
 
"The Hood"
Posts: 8521
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Per the API:


public class NullPointerException extends RuntimeException
Thrown when an application attempts to use null in a case where an object is required. These include:
Calling the instance method of a null object.
Accessing or modifying the field of a null object.
Taking the length of null as if it were an array.
Accessing or modifying the slots of null as if it were an array.
Throwing null as if it were a Throwable value.
Applications should throw instances of this class to indicate other illegal uses of the null object.


 
usman ahmad
Ranch Hand
Posts: 46
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Thanks Both of you!!
Regards,
Usman
 
Ranch Hand
Posts: 104
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I would call this as Software Bug.
All runtime Exceptions are puerly bugs.
It is possible to avoid this exceptions with proper care(i.e. checking the object before doing something with it.)
If you check the JDK documentation, All the subclasses from RuntimeException, clearly shows this.
Cheers
Siva
 
reply
    Bookmark Topic Watch Topic
  • New Topic