Queues and Exceptions

Question

Ok, I have a program that involves queues. Now, when the program checks if a queues is empty, if it is, it is supposed to handle an error. My prof uses "Underflow" , but I keep getting errors that it is undefined. I looked in the API and couldn't find anything in java.lang that says Underflow. What error out of java.lang should I use if the queue is empty?
Here is some code so you can see what I mean:
public int getFront() throws underflow
if (! isEmpty())
throw new Underflow("Empty queue"); <---------
return array[front];
try
while (! Subqueue0.isEmpty());
int extract = Subqueue0.dequeue();
Master.enqueue(extract);
} catch(Underflow e){} <--------

Answer 1

You can create your own exceptions in Java like
public class UnderFlowException extends Exceptionto handle several kinds of faults. Seems like your Prof has done so.