User-defined exceptions

[Shilong Zheng]

Hi,

I get the following error when i run my program

java.lang.NoClassDefFoundError: 24
Exception in thread "main"

Below is my program, kindly advise where did i go wrong... thanks..

import java.util.*;

public class FactorException extends Exception{

public FactorException(int x,int y) {
System.out.println("Exception thrown : "+y+" is not a factor of "+x);
}

public static void main(String[] args) {
int n1 = Integer.parseInt(args[0]);
int n2 = Integer.parseInt(args[1]);
try{
factor(n1,n2);
}catch(FactorException e){
System.out.println(e);
}
}

static void factor(int a, int b) throws FactorException{
if(b%a == 0){
System.out.println(b+" is a factor of "+a);
}else throw new FactorException(a,b);
}
}

Regards
Shilong

[Ernest Friedman-Hill]

Looks fine to me. Are you sure you're specifying the name of your class and not just passing the numeric arguments to "java"?

  [ejfried@asllinux tmp]$ java 24 48
  Exception in thread "main" java.lang.NoClassDefFoundError: 24
 
  [ejfried@asllinux tmp]$ java FactorException 24 48
  48 is a factor of 24

[Shilong Zheng]

Quote "Are you sure you're specifying the name of your class and not just passing the numeric arguments to "java"?"

Hi,

Pardon me for my ignorance.. i don't really understand your question.. you seem to get the same output for the first run also.. kindly advise further.. thanks...

java.lang.NoClassDefFoundError: 24
The number 24 seems to be pointing to my first command line input..


Regards
Shilong

[Ernest Friedman-Hill]

The first run is a deliberate example of how to produce the error by typing the wrong thing -- I deliberately left out the name of the class, and you see how I get the same error as you. If I include the name of the class, as shown in the second example, it works.

[Shilong Zheng]

Thanks a million, i got it..

[Shilong Zheng]

I tested out my program and it exits once it catches the exception, but i need it to continue till the end of the program even after catching exceptions. Kindly advise how to....

import java.util.*;

public class FactorException extends Exception{

public FactorException(int x,int y) {
System.out.println("Exception thrown : "+y+" is not a factor of "+x);
}

public static void main(String[] args) {
int n1 = Integer.parseInt(args[0]);
System.out.println("Student id : T6194898");
try{
for(int g=1; g<args.length; g++){
int n2 = Integer.parseInt(args[g]);
factor(n1,n2);
}
}catch(FactorException e){
System.out.println(e);
}
}

static void factor(int a, int b) throws FactorException{
if(a%b == 0){
System.out.println(b+" is a factor of "+a);
}else throw new FactorException(a,b);
}
}

Thank you and regards
Shilong

[Darin Niard]

I don't really understand what you mean. The catch you have is the end of the program. Your program seems to run fine for me.

P.S. Use code tags.
[ July 07, 2004: Message edited by: Darin Niard ]

[Ernest Friedman-Hill]

If you look at your code, you'll see that there's nothing after the catch block -- i.e., this program does continue to the end after catching the exception, there just isn't any more to do.

As a general pattern, if you want a loop to abort after an error, then you write

try {
  while (something)
    doSomething();
} catch(Whatever ex) {
  // handle error
}

But if after an error, you want to continue with the next iteration of the loop, then you write, instead

while (something) {
  try {
    doSomething();
  } catch(Whatever ex) {
    // handle error
  }
}

In the latter case, the try/catch block is inside the loop; after the catch block finishes, the loop simply continues.

[Shilong Zheng]

I need the program to finish all the inputs from the command line even if the exception is caught in between the inputs...

i tried many conditions for the 'while' loop but it seems like no matter what conditions i use, the 'while' loop will repeat only the 'for' loop and the 'for' loop will still exit when the exception is caught... Any suggestions for the while loop condition???


Thank you!!!

[Ernest Friedman-Hill]

I've just used a "while" loop to illustrate the principle. You would do the same thing with your "for" loop -- i.e., move the try block inside of it. There's no need for you to add a "while" loop.

[Shilong Zheng]

Roger... i am kinda slow sometimes... it works now.. just that this error appears every time i run the program... it's abit too profound to me.. any advise...

java.lang.NumberFormatException: FactorException
at java.lang.Integer.parseInt(Integer.java:409)
at java.lang.Integer.parseInt(Integer.java:458)
at FactorException.main(FactorException.java, Compiled Code)
Exception in thread "main"


A million thanks........

[Ernest Friedman-Hill]

When parseInt() is passed an argument that isn't a String, it will throw NumberFormatException; you're not catching that anywhere, so the exception will be printed and the program will stop. Based on the error message, it looks like your program is getting "FactorException" as an argument -- i.e., you're running something equivalent to

java FactorException FactorException 1 2 3

which brings us back to your first post in this thread!

[Ilja Preuss]

Originally posted by Ernest Friedman-Hill:
When parseInt() is passed an argument that isn't a String, it will throw NumberFormatException;

"that isn't a String representing a number" is what you probably wanted to say, isn't it?

[Ernest Friedman-Hill]

It is indeed, my friend.

[Shilong Zheng]

Quote:

Are you sure you're specifying the name of your class and not just passing the numeric arguments to "java"?

code:
---------------------------------------------------------------------------

[ejfried@asllinux tmp]$ java 24 48 Exception in thread "main" java.lang.NoClassDefFoundError: 24
[ejfried@asllinux tmp]$ java FactorException 24 48 48 is a factor of 24

---------------------------------------------------------------------------

Roger, I totally understand your last thread, but I find this abit weird, previously when i wrote programs to accept inputs from command line, i do not have to include the name of the class like example two above and it still works.. but now i have to include the class name in the command line no matter what.. an explanation???

[Darin Niard]

I doubt it ever worked like that. You have to specify the class name so that the JVM knows what class it needs to run. How else would it know? Think about it.

[Mike Curwen]

Perhaps they were a c/c++ programmer in their previous life ?