I/O problem from Amit poddar's test

[Praveen Kumar]

Hi all,
this question is from Amit poddar's moch test. The answer is" b".
but my question is why not Ans: a, becoz according to RHE(PAge no.
379)
"The File must describe a directory not a file." so this would be a
compile time error as File has argument "12345.msg" that is a file not
a dir.
please explain me.
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Q40) What will be the output if
Consider a directory structure like this (NT or 95)
C:\JAVA\12345.msg --FILE
\dir1\IO.class -- IO.class is under dir1
import java.io.*;
public class IO {
public static void main(String args[]) {
File f = new File("12345.msg");
String arr[] = f.list();
System.out.println(arr.length);
}
}
a) Compiler error as 12345.msg is a file not a directory
b) java.lang.NullPointerException at run time
c) No error , but nothing will be printed on screen
***********************


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Praveen Kumar
Mumbai ,India
email: [e-mail]

[Stephanie Grasson]

Praveen,
This is from the Java 2 specifications from Sun:
public String[] list()
Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.
If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of strings is returned, one for each file or directory in the directory.
I think the reason the answer is given as b is because, like you said, 12345.msg is NOT a directory. Therefore,

String arr[] = f.list();

should return null.
In the next line, they try to access arr.length with a null, hence the exception.
Hope this helps.
Stephanie

[Praveen Kumar]

Stephanie, Thanx for replying.

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Praveen Kumar
Mumbai ,India
email: [e-mail]

[hanmeng]

Hi, Could you please e-mail Amit poddar's mock exam to me:
[e-mail]
thank you very much!
Hanmeng