About Question enthuware.ocajp.i.v7.2.826 :

[ETS User]

According to the explanation, when it uses "System.out.println(exception)", a track trace is not printed and just the name of the exception class and the message is printed so... why is the option A and not the option C???
In option A, if I am not wrong, a track trace is printed, isn't?


Thanks in advance.

[dtchky]

Code: Select all

        int[] array = new int[10];
        array[10] = 1000;

The code above throws an ArrayIndexOutOfBoundsException before it ever reaches doAnotherTest, thus the answer is A and not C - the program is not throwing "MyException" since it crashes out before it reaches that piece of the code.

[javanaut]

According to the explanation, when it uses "System.out.println(exception)", a track trace is not printed and just the name of the exception class and the message is printed so... why is the option A and not the option C???
In option A, if I am not wrong, a track trace is printed, isn't?


Thanks in advance.

Yes, I was disturbed by this as well. The explanation says that a stack trace is not printed but if I comment out the System.out.println(me) and add me.printStackTrace() the exact same output is printed to the console.

This definitely needs to be edited as far as explaining the answer since a stack trace is printed and not just the name of the exception class and its string argument.



Regards,

Javanaut

[admin]

Hello,
The explanation is correct. The stack trace is being printed here NOT because of the println (which is never even invoked) but because the exception thrown at array[10] = 1000 is never caught by the catch block and is propagated out of the main method. It is the JVM's uncaught exception handler that prints the stack trace.

HTH,
Paul.

[javanaut]

Hi Paul,

Ah, yes this explanation makes sense. Thank-you for explaining this. That is tricky.

Regards,

Javanaut

[yeffayeffa]

Hello,
The explanation is correct. The stack trace is being printed here NOT because of the println (which is never even invoked) but because the exception thrown at array[10] = 1000 is never caught by the catch block and is propagated out of the main method. It is the JVM's uncaught exception handler that prints the stack trace.

HTH,
Paul.

Hallo, i dont't understand why ArrayIndexOutOfBounds Exception is never by caught by MyException. MyException extends Exception so it could intercept any exception but probably ii'm wrong doing this reasoning.

thanks

[admin]

MyException extends Exception but ArrayIndexOutOfBounds doesn't extend MyException. In other words, ArrayIndexOutOfBounds is-not-a MyException and so it cannot be caught by catch(MyException).
To know if a handler can catch a particular exception, you can check whether the exception that you want to catch satisfies the is-a test. For example, if you have catch(ExA a), and if the exception that is thrown is of class ExB, then ExB will be caught by the catch only if ExB is-a ExA is satisfied.

HTH,
Paul.

[yeffayeffa]

ok,now it's very clear. i was missing the "is-a" relationship. But ArrayIndexOutOfBoundsException is a subclass of IndexOutOfBoundException that is a subclass of RunTimeException that is a subclass of Exception. So ArrayIndexOutOfBoundsException is not a subclass of Exception ?

[apanah]

ok,now it's very clear. i was missing the "is-a" relationship. But ArrayIndexOutOfBoundsException is a subclass of IndexOutOfBoundException that is a subclass of RunTimeException that is a subclass of Exception. So ArrayIndexOutOfBoundsException is not a subclass of Exception ?

I had the same thought - can you respond on this?

[admin]

Please see attached class diagram. A catch block that catches MyException can only catch a MyException i.e. any class that is-a MyException, which means MyException and any of its subclasses.

From the class diagram you can see that ArrayIndexOutOfBoundsException is not a MyException. ArrayIndexOutOfBoundsException certainly is-a Exception but not MyException.

Therefore, the catch block in main() will not be able to catch ArrayIndexOutOfBoundsException, which is what the explanation to option 1 says.

exception_hierarchy.png (17.64 KiB) Viewed 6776 times

If there were another exception class SomeOtherImaginaryException that extended from MyException, and if doTest() method threw that exception, then catch(MyException) would have caught it.

HTH,
Paul.

[apanah]

Very clear - thanks!