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ssaa
Guest
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 Posted: Sat Apr 03, 2004 8:46 am Post subject: problem in Array -- Help please |
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Hi,
when i try to call the following class function "set_world(String w)"
from my main class, i am always getting error "error found". it looks
like the problem is with String array "worlds". but i cannot understand.
can anyone figure out the problem and explain little bit.
Thanks alot.
***********************************************************
import java.io.*;
import java.lang.*;
import java.util.*;
class operations
{
private String[] worlds;
operations(){ }
public void set_world(String w)
{
int count = 0;
try
{
worlds[count] = "ABCD";
}catch ( Exception ee)
{System.out.println("error found"); }
}
public String[] get_world()
{
return worlds;
}
}
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ssaa
Guest
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| Posted: Sat Apr 03, 2004 8:57 am Post subject: Re: problem in Array -- Help please |
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ALso please note that i am looking for dynamic array .
Thanks
ssaa wrote:
| Quote: | Hi,
when i try to call the following class function "set_world(String w)"
from my main class, i am always getting error "error found". it looks
like the problem is with String array "worlds". but i cannot understand.
can anyone figure out the problem and explain little bit.
Thanks alot.
***********************************************************
import java.io.*;
import java.lang.*;
import java.util.*;
class operations
{
private String[] worlds;
operations(){ }
public void set_world(String w)
{
int count = 0;
try
{
worlds[count] = "ABCD";
}catch ( Exception ee)
{System.out.println("error found"); }
}
public String[] get_world()
{
return worlds;
}
}
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Christophe Vanfleteren
Guest
|
| Posted: Sat Apr 03, 2004 9:04 am Post subject: Re: problem in Array -- Help please |
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ssaa wrote:
| Quote: | Hi,
when i try to call the following class function "set_world(String w)"
from my main class, i am always getting error "error found". it looks
like the problem is with String array "worlds". but i cannot understand.
can anyone figure out the problem and explain little bit.
Thanks alot.
***********************************************************
import java.io.*;
import java.lang.*;
import java.util.*;
class operations
{
private String[] worlds;
operations(){ }
public void set_world(String w)
{
int count = 0;
try
{
worlds[count] = "ABCD";
}catch ( Exception ee)
{System.out.println("error found"); }
}
public String[] get_world()
{
return worlds;
}
}
|
First of all, try to follow the naming conventions in your code:
http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html
The problem you're having, is that you're trying to use an array of Strings
that is not instantiated (so it is still null).
So change the line
private String[] worlds;
to
private String[] worlds = new String[SIZE_YOU_NEED];
You also do something very bad when catching the Exception. Instead of
seeing the actual error, you now only see your own message. At the very
least, do something like ee.printStacktrace(), which would have shown the
specific error you were having (NullPointerException), and on what line it
was.
--
Kind regards,
Christophe Vanfleteren
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ssaa
Guest
|
| Posted: Sat Apr 03, 2004 9:10 am Post subject: Re: problem in Array -- Help please |
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|
Thanks alot for the hint, But As you said i need to use
private String[] worlds = new String[SIZE_YOU_NEED];
i was wondering, is there any way to create a dynamic array because my
array size can vary. what is your suggestion for using Vector for
storing string ?
Thanks once again.
=***********************************************
Christophe Vanfleteren wrote:
| Quote: | ssaa wrote:
Hi,
when i try to call the following class function "set_world(String w)"
from my main class, i am always getting error "error found". it looks
like the problem is with String array "worlds". but i cannot understand.
can anyone figure out the problem and explain little bit.
Thanks alot.
***********************************************************
import java.io.*;
import java.lang.*;
import java.util.*;
class operations
{
private String[] worlds;
operations(){ }
public void set_world(String w)
{
int count = 0;
try
{
worlds[count] = "ABCD";
}catch ( Exception ee)
{System.out.println("error found"); }
}
public String[] get_world()
{
return worlds;
}
}
First of all, try to follow the naming conventions in your code:
http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html
The problem you're having, is that you're trying to use an array of Strings
that is not instantiated (so it is still null).
So change the line
private String[] worlds;
to
private String[] worlds = new String[SIZE_YOU_NEED];
You also do something very bad when catching the Exception. Instead of
seeing the actual error, you now only see your own message. At the very
least, do something like ee.printStacktrace(), which would have shown the
specific error you were having (NullPointerException), and on what line it
was.
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Christophe Vanfleteren
Guest
|
| Posted: Sat Apr 03, 2004 9:33 am Post subject: Re: problem in Array -- Help please |
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|
ssaa wrote:
| Quote: | Thanks alot for the hint, But As you said i need to use
private String[] worlds = new String[SIZE_YOU_NEED];
i was wondering, is there any way to create a dynamic array because my
array size can vary. what is your suggestion for using Vector for
storing string ?
|
Please don't toppost.
One of the classes of the Collections framework will do:
http://java.sun.com/docs/books/tutorial/collections/
An implementation of the List interface (like ArrayList) resembles a
resizable array the most.
--
Kind regards,
Christophe Vanfleteren
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