K&B Page 382 Exception

[Harikrishna Gorrepati]

Hi, There are several exceptions(ClassCast, IllegalState, NullPointer, StackOverflow etc..) listed in page 382 K & B. How do we know that these exceptions will be thrown by JVM or programmatically.

[Stephan van Hulst]

By reading the contract of a class or method you use. It should tell which exceptions it throws and when.

[Harikrishna Gorrepati]

Hi Stephan, I am under the impression that Checked Exceptions are thrown programmatically and Un-checked(Runtime) Exceptions thrown by JVM ? Could you please advice if this statement is correct or not ?

[Stephan van Hulst]

No. While I'm not sure if the JVM itself throws exceptions (I imagine it throws stuff like OutOfMemoryError and InternalError), most exceptions are thrown programmatically (if you can even consider Error's thrown by the JVM to be non-programmatic). It doesn't really matter, you shouldn't care.

The fact of the matter is that regardless of where exactly exceptions have their origin, they 'bubble up' until they are either catched or thrown by the main method. This means that you should check the contract of any methods that you call, to see whether they are capable of throwing a certain exception. Methods that you write yourself can also throw exceptions, if you want them to. These can be both checked and runtime exceptions.

[Abimaran Kugathasan]

Harikrishna Gorrepati wrote:Hi Stephan, I am under the impression that Checked Exceptions are thrown programmatically and Un-checked(Runtime) Exceptions thrown by JVM ? Could you please advice if this statement is correct or not ?

I think, JVM throws only unchecked exceptions. But, we can programmatically throw checked and unchecked exceptions. For example, IllegalArgumentException, IllegalStateException & NumberFormatException are all unchecked exceptions, but they are thrown programmatically, not by JVM.

[Bert Bates]

Would you guys make a "JVM vs Programmatic" distinction between an IllegalArgumentException and an ArrayIndexOutOfBoundsException?

[swaraj gupta]

I think its not about throwing the exceptions, its about catching the exceptions.

1. Compiler will not compile your file(.java) until you handle the checked exceptions as these are compulsory to handle....
2. However unchecked exceptions there are no restrictions over them you can manage them in whatever way you want...
3. And errors, we should not handle them let the JVM handle them...

Well it would surely be better if you code and try different combinations of them ..if you still have some problem then you can discuss....

[Harikrishna Gorrepati]

int i = Integer.parseInt("ABC"); throws IllegalArgumentException(if not caught by its subclass i.e., NumberFormatException).
String[] stringArray = new String[] {"Hi", "Hello"}; If we try to fetch any value from 2nd index(3rd element), we get ArrayIndexOutofBoundsException.
I personally feel that because of programmatic errors, JVM throws above 2 Runtime Exceptions.

Book says IllegalStateException (IS-A RuntimeException) thrown by Programmatically and ArrayIndexOutofBoundsException(IS-A RuntimeException) thrown by JVM.
It is hard to figure out the differences why one throws Programmatically while the other one throws by JVM.
Also, Why AssertionError (IS-A Error) thrown by Programmatically
Confusing...

Bert Bates wrote:Would you guys make a "JVM vs Programmatic" distinction between an IllegalArgumentException and an ArrayIndexOutOfBoundsException?

[swaraj gupta]

Programmatically throwing the exception means you are manually creating the object of an exception and throwing it. like this..

public void anyMethod() throws Exception 
{
   Exception e=new Exception();
   throw e;
}

If you are not doing so, then the JVM does it for you for exceptions that generates at run time and this no more would be considered as Programmatically thrown exception....

[Bert Bates]

Hmmm...

Let me ask this a different way:

Imagine you were writing a utility class that other programmers might use later, can you envision:

1 - Somewhere in your code you decide to throw your own IllegalArgumentException?

2 - Somewhere in your code you decide to throw your own ArrayIndexOutOfBoundsException?

[Harikrishna Gorrepati]

Bert Sir, I am not sure. Could you please explain how to differentiate..I am not able to envision.

[Bert Bates]

Let's say I want to write a method for other programmers to use. Let's say that the idea of this method is to convert hexadecimal numbers into binary. If someone is using my method and they pass my method an argument that isn't formatted as a hexadecimal string, I might want to throw an IllegalArgumentException. That's me, a programmer, throwing an exception programmatically.

Now, I can't think of a similar situation where I'd want to throw an ArrayIndexOutOfBoundsException. Typically, that exception is thrown by the JVM to indicate some sort of bug in some code that's messing with arrays.

hth,

Bert