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String Operation

 
Greenhorn
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hi kindly tell me why I am getting Nullpointer Exception in following code.

(1) Vector vector=(some resultset from DB);
String str = "";
str = vector.elementAt(0).toString();

==========

Following code not giving exception

(2) Vector vector=(some resultset from DB);
String str="";
str = str+vector.elementAt(0).toString();

Although i have done with coding number (2), but i want to know the technical reason for failure of coding number (1).

Thanks & Regards
 
Ranch Hand
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Hi Lucky,

Couldn't understand why the second method work. It doesn't make sense. If the vector is empty and elementAt(0) is called, java.lang.ArrayIndexOutOfBoundsException is thrown. If the vector is not empty and the elementAt(0) is called successfully, an object will be returned. A NullPointerException is thrown when trying to access members of a null object.

I wrote a simple code to experiment it.




Could the problem of NullPointerException caused by other part of the code?

Joyce
[ November 02, 2004: Message edited by: Joyce Lee ]
 
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v.elementAt(0) is returning null.
Your second diagnosis is false.
You shouldn't be using a Vector.
 
Consider Paul's rocket mass heater.
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