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NullPointerException - could somebody explain why ?  RSS feed

 
roni suvanto
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Posts: 13
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Hello,
first time this year with Java and seems like I've forgotten some basic concepts about OOP
I'm coding a simple ascii-based flat-file database as a homework and I didn't get very far before first problems appeared.
Exception in thread "main" java.lang.NullPointerException
at Yearclass.ask(Register.java:103)
at Register.main(Register.java:7)
Could somebody be kind enough to tell me, what's wrong with the following code ?
 
Maulin Vasavada
Ranch Hand
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hi roni
in YearClass's Students[] u did allocated memory for the array but not for the individual elements which are again objects of Student class.
so in the ask() method's for loop when you invoke method on students[i].ask() it gives u null pointer as students is allocated but not students[i].
somewhere u shd have,
for(int i=0; i < MAX; i++)
students[i] = new Student();
u know..
regards
maulin
 
roni suvanto
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Originally posted by Maulin Vasavada:
hi roni
so in the ask() method's for loop when you invoke method on students[i].ask() it gives u null pointer as students is allocated but not students[i].

Thank you Maulin. It works fine now. Looks like I should brush up with some basic OOP concepts.
- Roni
 
It is sorta covered in the JavaRanch Style Guide.
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