Illegal State Exception

[Sushant Kaushik]

Hello Ranchers,
I am new to this forum. I have a doubt about K &B Self test Chapter 5 Q16. Below is the question -

Which are most typically thrown by an API developer or an application developer as opposed to being thrown by the JVM? (Choose all that apply.)
A. ClassCastException
B. IllegalStateException
C. NumberFormatException
D. IllegalArgumentException
E. ExceptionInInitializerError

Answer is - B,C & D.

I agree with C & D. But I am not able to understand how B is also correct answer. I have never come across any code where we throw IllegalStateException as part of our programming. Hope to get ot clarified from the Ranchers.

Thanks,
Sushant

[Mike Simmons]

[Sushant]: I have never come across any code where we throw IllegalStateException as part of our programming.

The intent of the question appears to be: which of these exceptions are thrown by API or application developers more often than they are thrown by the JVM? So to answer this, you need to know something about:

How often is this exception thrown by API or application developers?

How often is this exception thrown by the JVM?

Now if you've never encountered this exception ever in any context, you probably need to study more before you take the exam - particularly, study threads and the wait()/notify() methods.

To answer this question, I think about the fact that I can't think of any circumstance where the JVM throws this exception. But I can think of several circumstances where an API developer (from Sun) has chosen to throw this exception. Two examples would be in the API for Object's wait() and notify() methods, which are part of the exam objectives, as I recall. So I would say that it's more likely that this exception will be thrown by an API developer, as opposed to the JVM. Even if event A is rare, if event B never occurs, then A is more likely than B. It's not enough to say "I've never heard of A happening" - you also need to consider whether you've ever heard of B happening. If you've never heard of either, then you need more data - which means more studying.

[Punit Singh]

Sushant very good question

I tried to solve this.
See code:

  import java.util.Formatter;
 
 
public class IllegalStateExceptionInFormatter {
public static void main(String[] args) {
StringBuffer sb=new StringBuffer();
Formatter f=new Formatter(sb);
f.close();//[B]I have closed formatter here[/B]
//[B]but i am using, this is illegal state and developer has handled this situation[/B]
f.format("My name is : %s", "Sushant");
System.out.println(sb);
}
}  

When you run this program, you will get

Exception in thread "main" java.util.FormatterClosedException

and this FormatterClosedException is the child of IllegalStateException.

public class FormatterClosedException extends IllegalStateException

Here this exception is not thrown by JVM, it is thrown programmatically by the Formatter API developers, if you see the code of Formatter API, you will find this method get called.

private void ensureOpen() {
if (a == null)
throw new FormatterClosedException();
}

You can see the developer is throwing this exception that is the child of IllegalStateException. Any doubt ???
[ December 21, 2008: Message edited by: punit singh ]

[Punit Singh]

IllegalStateException here you will find lots of example where developers has used this exception.

[Duran Harris]

Hmmm...I did this question yesterday...
I only chose Number Format Exception and Illegal Argument Exception..and I'm pretty sure that Master Exam said I was correct!

[Sushant Kaushik]

Thanks Punit & Mike. The explanation clears my doubt