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NullPointerException

Posted on 1998-07-22
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Last Modified: 2010-05-18
I recently download a working applets and after running it without changing any codes, it give me an Java.Lang.NullPointerException error.

Anbody know why error is this and what causes it?
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Question by:wizlor
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dryang earned 300 total points
ID: 1227791
This is something from the JDK 1.1.6 documentation.

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.

This can be cause by a few things
1) Bad programming practices, where the programmer does not take care with
      - arry lengths
      - vector sizes
      - accesing empty Vectors. eg using the elementAt mehtod.( I did theis before :) )

2) Exception cases
     - plain bad luck when your data length values get corrupted and your pointers point to nowhere(did they mention that java had no pointers?)...

do go over the codes and see if you can spot the bug (usually in the looping sections, for and while loops)

regards
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Author Comment

by:wizlor
ID: 1227792
Thx for your help.
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Expert Comment

by:dryang
ID: 1227793
hi wizlor,
you're welcome
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